Particle Physics seminar archive - Department of Theoretical Physics

Weekly seminars of the Department of Theoretical Physics

Location: 2nd floor, 2.54, Novobatzky room

Archive from 2014 to current, most recent last.


  • 10 September 2014, Mate Lencses (Eotvos University, Hungary)

    Excited state TBA and renormalized TCSA in the scaling Potts model slides

    We consider the field theory describing the scaling limit of the Potts quantum spin chain using a combination of two approaches. The first is the renormalized truncated conformal space approach (TCSA), while the second one is a new thermodynamic Bethe Ansatz (TBA) system for the excited state spectrum in finite volume. For the TCSA we investigate and clarify several aspects of the renormalization procedure and counter term construction. The TBA system is first verified by comparing its ultraviolet limit to conformal field theory and the infrared limit to exact S-matrix predictions. We then show that the TBA and the renormalized TCSA match each other to a very high precision for a large range of the volume parameter, providing both a further verification of the TBA system and a demonstration of the efficiency of the TCSA renormalization procedure. We also discuss the lessons learned from our results concerning recent developments regarding the low-energy scattering of quasi-particles in the quantum Potts spin chain. See arXiv:1405.3157

  • 17 September 2014, Marton Kormos (BME, Hungary)

    Correlations after quantum quenches in the XXZ spin chain: Failure of the Generalized Gibbs Ensemble slides

    The topic of thermalization of isolated quantum systems has enjoyed a lot of attention lately, partially due to the fast evolving experimental techniques in cold atom systems. Until recently, it was generally accepted that even completely isolated many-body systems self-thermalize to a certain extent: their evolution from a non-equilibrium initial state leads to a local thermal equilibrium (Gibbs ensemble) or to the Generalized Gibbs Ensemble (GGE) for integrable systems that have extra conserved quantities. We studied the non-equilibrium time evolution of the integrable spin-1/2 anisotropic Heisenberg (XXZ) spin chain, and we found that various short-ranged spin correlators in the long-time limit deviate significantly from predictions based on the GGE hypothesis. By computing the asymptotic spin correlators within the recently proposed quench action formalism, however, we find excellent agreement with the numerical data. We therefore conclude that the GGE cannot give a complete description even of local observables. This surprising result reopens the quest for the correct statistical description of the equilibrium state of integrable systems.

  • 24 September 2014, Attila Pasztor (Eotvos University, Hungary)

    Heavy quarkonium at finite temperature from 2+1 flavour lattice QCD slides

    Heavy quarkonium states are of great interest as a possible thermometer of hot QCD matter. For this idea to work, the determination of the dissociation temperatures of the different states is necessary. In this talk I will review some recent results from lattice QCD with 2+1 dynamical quarks that gives input to this long-standing problem. In the first part of the talk I will discuss the direct Maximum Entropy determination of spectral functions and to how much extent the lattice data depend on the heavy quark diffusion coefficient. In the the second part I will present continuum results on the static quark-antiquark pair free energies and the electric and magnetic screening masses in the QGP.

  • 1 October 2014, Guido Franchetti (Heriot-Watt University, UK)

    Geometric models of matter slides

    Geometric models of matter is a framework introduced by Atiyah, Manton and Schroers with the aim of modelling particles by means of 4-dimensional Riemannian manifolds. In this talk I will review the original proposal as well as more recent work about ALF gravitational instantons as models for multi-particle systems. Harmonic forms on these spaces have interesting properties which will be also discussed.

  • 8 October 2014, Gergo Zarand (BME, Hungary)

    Mott skyrmions: stabilizing the false vacuum slides

    Topological excitations keep fascinating physicists since many decades. While individual vortices and solitons emerge and have been observed in many areas of physics, their most intriguing higher dimensional topological relatives, skyrmions and magnetic monopoles remained mostly elusive. Here we propose that loading a three-component nematic superfluid such as 23Na into a deep optical lattice and thereby creating an insulating core, one can create topologically stable skyrmion textures and investigate their properties in detail. We show furthermore that the spectrum of the excitations of the superfluid and their quantum numbers change dramatically in the presence of the skyrmion, and they reflect the presence of a trapped monopole, as imposed by the skyrmion's topology. Signatures of the presence of the skyrmion in time of flight experiments as well as experimental protocols to create it shall also be discussed.

  • 15 October 2014, Istvan Nandori (ATOMKI, Hungary)

    Renormalization scheme-dependence in the FRG Method slides

    The Functional Renormalization Group (FRG) method has been constructed to perform the renormalization non-perturbatively and it has been successfully applied in many cases over the last four decades. The modern form of FRG is the Wetterich equation which can be related to the previously introduced Wegner-Houghton and Polchinski equations by the appropriate choice of the so called regulator function, i.e. the renormalization scheme. FRG equations are integro-differential equations for functionals thus their solutions require approximations. However, the approximated FRG equations depend on the choice of the regulator function thus the predictions for physical quantities could become scheme-dependent too. I discuss this renormalization scheme-dependence of the FRG method in the context of the so called compactly supported smooth (CSS) regulator function introduced recently.

  • 22 October 2014, Gabor Somogyi (CERN, Switzerland)

    Colorful NNLO -- Higher order QCD corrections via local subtraction slides

    At the LHC very high energy proton-proton collisions are measured at a level of precision which demands that the theory predictions be computed at higher orders in perturbation theory. In recent years the precision frontier for QCD calculations has moved beyond next-to-leading order and today fully differential results at next-to-next-to-leading order accuracy are available for a handful of processes. One serious bottleneck which hampers the straightforward evaluation of cross sections at higher perturbative orders is the presence of infrared singularities in intermediate stages of the computation. One possible way of dealing consistently with infrared singularities is through a so-called subtraction scheme. In this talk I will describe the Colorful NNLO algorithm, a completely local subtraction scheme for fully differential predicitions at NNLO in QCD. I will give an overview of the main conceptual issues that need to be addressed as well as present some technical aspects and a first application of the method.

  • 29 October 2014, Janos Polonyi (University of Strasbourg, France)

    Classical and quantum effective theories slides

    A generalization of the action principle of classical mechanics, motivated by the Closed Time Path (CTP) scheme of quantum field theory, is presented to deal with initial condition problems and dissipative forces. The similarities of the classical and the quantum cases are underlined. In particular, effective interactions which describe classical dissipative forces represent the system-environment entanglement. The relation between the traditional effective theories and their CTP extension is briefly discussed and few qualitative examples are mentioned.

  • 5 November 2014, Zoltan Bajnok (Wigner Center, Hungary)

    Integrability for 2 and 3pt functions in AdS5/CFT4 slides

    In my talk I review the strategy of the integrable bootstrap method. I explain how it determines the spectrum of string states on AdS5 x S5, i.e. the scaling dimensions of single trace operators in planar N=4 SYM. I emphasize its non-perturbative nature and that it starts at infinite volume and systematically calculates the finite size corrections based on the infinite volume scattering data. In the second part of the talk I outline a similar program to determine the 3pt functions via the bootstrap method.

  • 12 November 2014, Gergely Marko (Eotvos University, Hungary)

    Bose-Einstein condensation and Silver Blaze in the 2-loop Phi-derivable approximation slides

    We numerically study the chemical potential-temperature phase diagram of the O(2) model within the 2-loop truncation of the Phi-derivable formalism. We find that different parameters allow for a phase transition of either SSB or BEC type. In the BEC case we observe the Silver Blaze phenomenon, which we understand and generalize using analyticity arguments. We compare our results both with the Hartree-Fock approximation and with lattice simulations. We discuss the loss of solution strongly connected with the Goldstone-theorem.

  • 19 November 2014, Gabor Etesi (BME, Hungary)

    Gravity as a four dimensional algebraic quantum field theory slides

    Based on an indefinite unitary representation of the diffeomorphism group of an oriented 4-manifold an algebraic quantum field theory formulation of gravity is exhibited. More precisely the representation space is a Krein space therefore as a vector space it admits a family of direct sum decompositions into orthogonal pairs of maximal definite Hilbert subspaces coming from the Krein space structure. It is observed that the C*-algebra of bounded linear operators associated to this representation space contains algebraic curvature tensors. Classical vacuum gravitational fields i.e., Einstein manifolds correspond to quantum observables obeying at least one of the above decompositions of the space. In this way classical general relativity exactly in 4 dimensions naturally embeds into an algebraic quantum field theory whose net of local C*-algebras is generated by local algebraic curvature tensors and vector fields. This theory is constructed out of the structures provided by an oriented 4-manifold only hence possesses a diffeomorphism group symmetry. Motivated by the Gelfand--Naimark--Segal construction and the Dougan--Mason construction of quasi-local energy-momentum we construct certain representations of the limiting global C*-algebra what we call the ``positive mass representations''. Finally we observe that the bunch of these representations give rise to a 2 dimensional conformal field theory in the sense of G. Segal.

  • 26 November 2014, Janos Balog (Wigner Center, Hungary)

    Walking in a 3-dimensional scalar toy model slides

    The O(N) scalar field theory in the large N limit is an ideal toy model exhibiting "walking" behavior, expected in some SU(N) gauge theories with a large number of fermion flavors. We study the model using lattice regularization and show that when the ratio of the particle mass to an effective 4-point coupling (with dimension mass) is small, the beta function associated to the running 4-point coupling is ?walking?. We show the robustness of the walking phenomenon by showing that it can also be observed by studying physical observables such as the scattering phase shifts and the mass gap in finite volume.

  • 17 December 2014, Kim Splittorff (Niels Bohr Institute, Copenhagen, Denmark)

    Complex Langevin in QCD with chemical potential larger than half the pion mass

    The complexification of gauge fields in the complex Langevin approach to QCD at non zero chemical potential drastically affects the Dirac spectrum. In particular, we show that the eigenvalues the Dirac operator in complex Langevin simulations of QCD at non-zero chemical potential must accumulate at the origin in order to support spontaneous breaking of chiral symmetry. This mechanism is exemplified through application of the complex Langevin method in chiral random matrix theory.

  • 28 January 2015, Chaiho Rim (Sogang University, South Korea)

    Some applications of random matrix models slides

    Random matrix models are used to describe (1) statistical variance of multivariables using Gaussian pontential (2) 2d quantum gravity using polynomial potential (3) regular and irregular conformal block using Penner-type (logarithmic) potential.

  • 11 February 2015, Fidel I Schaposnik Massolo (La Plata, Argentina)

    D5-brane boundary reflection factors slides

    a We compute the strong coupling limit of the boundary reflection factor for excitations on open strings attached to various kinds of D5-branes that probe AdS(5)xS(5). We study the crossing equation, which constrains the boundary reflection factor, and propose that some solutions will give the boundary reflection factors for all values of the coupling. Our proposal passes various checks in the strong coupling limit by comparison with diverse explicit string theory computations. In some of the cases we consider, the D5-branes correspond to Wilson loops in the k-th rank antisymmetric representation of the dual field theory. In the other cases they correspond in the dual field theory to the addition of a fundamental hypermultiplet in a defect.

  • 18 February 2015, Yunfeng Jiang (Saclay, France)

    Integrability in AdS/CFT : Three-Point Functions in N=4 SYM theory

    The discovery of integrability in the planar N=4 Super-Yang-Mills theory and its AdS dual has triggered a lot of progress in recent years. Equipped with powerful integrability based techniques, it is now possible to compute many interesting quantities such as the spectrum, Wilson loop and scattering amplitudes of the theory at any value of the coupling constant. In this talk, I will explain how to compute three-point functions in the planar N=4 SYM theory at tree level and one loop in perturbation theory using Bethe ansatz. I will also discuss the semi-classical limit and the comparison with the computation at strong coupling.

  • 25 February 2015, Robert Wald (Enrico Fermi Institute, Chicago)

    Dynamic and Thermodynamic Stability of Black Holes and Black Branes slides

    I describe work with with Stefan Hollands that establishes a new criterion for the dynamical stability of black holes in $D \geq 4$ spacetime dimensions in general relativity with respect to axisymmetric perturbations: Positivity of the canonical energy, $\mathcal E$, on a subspace of linearized solutions that have vanishing linearized ADM mass, momentum, and angular momentum at infinity and satisfy certain gauge conditions at the horizon implies mode stability. Conversely, failure of positivity of $\mathcal E$ on this subspace implies the existence of perturbations that cannot asymptotically approach a stationary perturbation. We further show that $\mathcal E$ is related to the second order variations of mass, angular momentum, and horizon area by $\mathcal E = \delta^2 M - \sum_i \Omega_i \delta^2 J_i - (\kappa/8\pi) \delta^2 A$. This establishes that dynamic stability of a black hole is equivalent to its thermodynamic stability (i.e., its area, $A$, being a maximum at fixed ``state parameters'' $M$, $J_i$). For a black brane, we prove that a sufficient condition for instability is the failure of the Hessian of $A$ with respect to $M$, $J_i$ to be negative, thus proving the Gubser-Mitra conjecture. We also prove that positivity of $\mathcal E$ is equivalent to the satisfaction of a ``local Penrose inequality,'' thus showing that satisfaction of this local Penrose inequality is necessary and sufficient for dynamical stability.

  • 25 February 2015, George Sparling (Pittsburgh)

    Searching for structure: A tribute to Doctor Zoltan Perjes - the universe, large and small.

    One hundred years after the final formulation of general relativity by Albert Einstein, the quest to comprehend his theory continues. Doctor Zoltan Perjes was a master of the theory, constantly stretching its boundaries. He would work in cosmology, the study of the whole universe, always being concerned with relating the abstract theory to measurable quantities, such as the Sachs-Wolfe effect. He would also work locally dealing with isolated bodies, such as stars, testing their stability and trying to construct realistic models. He had his own speciality the theory of space times with a timelike symmetry, for which he developed his beautiful triad formalism and the sub-theory of conformastat space-times.

    In this talk I will present two recent results of mine and my colleague Jonathan Holland, which I believe would have been dear to Zoltan's heart: First an analysis of Bach flat metrics of a split form: in particular it is proved that all such have a symmetry. Second a discussion of the new approach to cosmology that we have initiated in the last two years: in our basic model a key role is played by a timelike conformal symmetry. This new theory leads to a remarkable new picture of the relationship between local and global cosmology and brings to bear for the first time major modern mathematical tools: the theory of Fano manifolds.

  • 4 March 2015, Gabor Takacs (BME, Hungary)

    Form faktorok a lepcsohazbol slides

    Alyosha Zamolodchikov a sinh-Gordon modell termodinamikai Bethe Ansatz egyenletenek analitikus elfolytatasaval lepcsos renormalasi csoport folyamot konstrualt, amivel sikerult alternativ leirast adnia a konform minimalis modellek (multikritikus Ising modellek) kozotti cross-over folyamokra. Otletet a c-tetelen keresztul megfogalmazva eljarast adunk a cross-overt leiro terelmeletek egzakt form faktorainak konstrukciojara. A feltarulo struktura felveti annak lehetoseget, hogy szamos integralhato terelmelet egzakt form faktorait a bootstrap jelentette igen bonyolult matrix Riemann-Hilbert problema helyett egy, a TBA univerzalis megfogalmazasabol kapcsolodo diagrammatikus konstrukciobol megkonstrualjuk.

  • 11 March 2015, Tamas Kovacs (ATOMKI, Debrecen, Hungary)

    The chiral and the Anderson transition in QCD slides

    Recently we have been studying an Anderson-type localization-delocalization transition in the spectrum of the Dirac operator describing quarks in the quark-gluon plasma. In the talk I summarize the latest results about the properties of this transition and its possible implications on the thermodynamics of QCD and other QCD-like theories.

  • 18 March 2015, Peter Mati (BME, Hungary)

    The Vanishing Beta Function Curves from the Functional Renormalisation Group

    We will discuss the derivation of the so called Vanishing Beta Function curves which can be used to explore the fixed point structure of the theory under consideration. This can be applied to the O(N) symmetric theories essentially for arbitrary dimensions (D) and field component (N). We will show the restoration of the Mermin-Wagner theorem for theories defined in D <= 2 and the presence of the Wilson Fisher fixed point in 2<D<4. Triviality is found in D>4. Interestingly, one needs to make an excursion to the complex plane to see the triviality of the four dimensional O(N) theories. The large N analysis shows a new fixed point candidate in 4<D<6 dimensions which turns out to define an unbounded fixed point potential supporting the recent results by R. Percacci and G. P. Vacca. Corresponding paper: http://arxiv.org/abs/1501.00211

  • 1 April 2015, Peter Gnadig (Eotvos)

    Alkalmazhato-e a Biot--Savart-torveny nem zarodo "aramkorokre"?

  • 8 April 2015, Richard Szabo (Heriot-Watt University, UK)

    Nonassociative Quantum Mechanics slides

    We briefly review recent developments from string theory which suggest that non-geometric string backgrounds experience a nonassociative deformation of spacetime geometry. A geometrisation of this frame leads to a sigma-model for closed strings propagating in an effective target space that is the phase space of the original compactification manifold. Quantization of the sigma-model produces an explicit nonassociative star-product algebra on functions on phase space, which is related to the quantization of Nambu-Poisson structures. We use this formalism to develop a phase space formulation of nonassociative quantum mechanics, and demonstrate that, against all odds, a consistent formulation seems indeed possible. Our approach is completely quantitative and adds to previous qualitative discussions of nonassociativity in quantum mechanics, and it moreover avoids previous no-go theorems.

  • 22 April 2015, Peter Bantay (Eotvos)

    Replication identities in 2D Conformal Field Theory slides

    We discuss an approach to replication identities satisfied by conformal characters of a 2D CFT that links them with symmetries of symmetric products, providing a physics interpretation of the Hauptmodul property of Monstruous Moonshine.

  • 29 April 2015, Marietta Homor (Eotvos)

    Transport Coefficients and Thermalisation in Classical Field Theories slides

    Our first objective is to show a practical method for the determination of viscosity in classical, relativistic field theories. We will discuss the relevant physical quantities in thermalised systems by the example of Phi^4 theory. Furthermore, we recently observed that the thermalisation in itself has interesting properties e.g. the distributions thermalize in a much shorter scale than the temperature. Inspired by this, our second objective is to examine the thermalisation properties of Phi^4 theory from various initial conditions. We propose, that the first correction to the Maxwell-Boltzmann distribution is the Tsallis distribution.

  • 20 May 2015, Andreas Ringwald (DESY Hamburg)

    Ultralight Axion-Like Particles from Strings slides

    There are various puzzling observations in sastrophysics which may be explained by the existence of light axion-like particles (ALPs) with a tiny coupling to the known particles of the Standard Model. In this talk, we will discuss how such ALPs and their couplings to the Standard Model may arise naturally from ultraviolet extensions inspired by string theory.

  • 16 September 2015, Anna Zsigmond (MTA-Wigner)

    Studies of nuclear parton distribution functions in proton-lead collisions with the CMS experiment slides

    The purpose of the study of nuclear parton distribution functions (nPDFs) is two-fold. On one hand, it provides a handle on the initial state cold nuclear effects that can be separated from the final state effects of the hot and dense medium produced in nucleus-nucleus collisions at the LHC and RHIC. On the other hand, precise knowledge of nPDFs is required for understanding the mechanisms associated with nuclear binding from a QCD improved parton model perspective. The proton-lead collision data recorded by CMS in 2013 provides the best sample to constrain nuclear parton distribution functions in the previously unexplored high Q^2 and low Bjorken x region. Results from the CMS experiment on electroweak boson, charged hadron and jet production in proton-lead collisions will be presented.

  • 30 September 2015, Andras Laszlo (MTA-Wigner)

    A natural extension of the conformal Lorentz group in a field theory context slides

    In this talk a finite dimensional unital associative algebra is presented, and its group of algebra automorphisms is detailed. The studied algebra can physically be understood as the creation operator algebra in a formal quantum field theory at fixed momentum for a spin 1/2 particle along with its antiparticle. It shall be shown that the essential part of the corresponding automorphism group can naturally be related to the conformal Lorentz group. In addition, the non-semisimple part of the automorphism group can be understood as ``dressing'' of the pure one-particle states. The studied mathematical structure may help in constructing quantum field theories in a non-perturbative manner. In addition, it provides a simple example of circumventing Coleman-Mandula theorem using non-semisimple groups, without SUSY. preprint

  • 7 October 2015, Zoltan Bajnok (MTA-Wigner)

    Form factor approach to the string vertex slides

  • 14 October 2015, Andrey Slavnov (Steklov Mathematical Institute, Moscow)

    Soliton solutions of classical equations of motion in the modified Yang-Mills theory slides

    It is shown that classical solutions with finite energy exist in the modified formulation of Yang-Mills theory.

  • 21 October 2015, Yoichi Kazama

    AdS/CFT and integrability: Cognate structure at weak and strong coupling for three-point functions

  • 4 November 2015, Sona Pochybova (MTA-Wigner)

    High Momentum Particle identification with the HMPID detector at the CERN's ALICE Experiment slides

    The High Momentum Particle IDentification (HMPID) detector is a Ring Imaging CHerenkov (RICH) radiation detector within the ALICE experiment used to identify pions, Kaons and protons between 1.0 < pT < 5.0 GeV/c. It is used by the collaboration in several physics analyses as a supporting tool for the tracking detectors in the ALICE central barrel. In the first part of my talk I will show how the track-by-track particle identification is utilized to extend the pion identification range by 1 GeV/c in momentum. Further, I will show how this extension helps in the spectra and correlation analyses to cross-check the results. Such and independent cross-check not only strengthens the robustness of the experimental claims, moreover, it has the potential of decreasing the systematic errors connected to these analyses. In the second part of my talk I will discuss the physics implications of the results I obtained in the analysis of p/pi ratio, where protons and pions are identified using the HMPID. This ratio is extracted from the spectra analysis and the origins of it's value are studied in the correlation analysis.

  • 11 November 2015, Tamas Gombor (ELTE)

    Algebraic Bethe Ansatz for O(2N) sigma models with integrable diagonal boundaries slides

    The finite volume problem of the O(2N) sigma models with integrable diagonal boundaries on a finite interval is investigated. The double row transfer matrix is diagonalized by Algebraic Bethe Ansatz. The boundary Bethe Yang equations for the particle rapidities and the accompanying Bethe Ansatz equations are derived.

  • 18 November 2015, Robert Vertesi (MTA-Wigner)

    Recent results from the STAR experiment slides

    In ultrarelativistic heavy ion collisions, a phase transition occurs from hadronic matter into a state of deconfined quarks and gluons. Properties of this latter state of matter, dubbed as the strongly interacting Quark Gluon Plasma (sQGP) has been a subject of extensive measurements at the Relativistic Heavy Ion Collider (RHIC), which collides several types of heavy nuclei (eg. d+Au, Cu+Cu, Au+Au, U+U) with collision energies that range from \sqrt{s_{NN}}=7.7 to 200 GeV. The Solenoidal Tracker at RHIC (STAR) identifies particles and measures their properties in the full azimuth angle and in a wide rapidity range. STAR's beam energy scan (BES) program aims to understand the QCD phase diagram and search for the critical point, and includes a new fixed target program that extends the lower energy limit down to \sqrt{s_{NN}}=3.3 GeV. Heavy and light flavor probes, on the other hand, are used to understand the thermal and dynamical properties of the sQGP. Some of the most interesting recent heavy-ion results from STAR will be overviewed in this talk.

  • 25 November 2015, Miklos Horvath (MTA-Wigner)

    Liquid-gas crossover within a quasi-particles picture slides

    We consider an effective field theory description of quasi-particle excitations aiming to associate the transport properties of the system with the spectral density of states. Tuning various properties of the many-particle correlations, we investigate how robust microscopic features are translated into the macroscopic observables like shear viscosity and entropy density. The liquid-gas crossover is discussed using several counterexamples. We sketch the adaptability of the present examination to much more intricate questions, like transport in (continuum extrapolated) lattice QCD or in correlated solid state systems with condensate.

  • 2 December 2015, Gabor Sarosi (BME)

    Warped Weyl fermion partition functions

    Warped conformal field theories (WCFTs) are a novel class of non-relativistic theories. A simple, yet non-trivial, example of such theory is a massive Weyl fermion in (1+1)-dimensions, which we study in detail. We derive general properties of the spectrum and modular properties of partition functions of WCFTs. The periodic (Ramond) sector of this fermionic system is non-trivial, and we build two novel partition functions for this sector which have no counterpart in a two dimensional CFT. The thermodynamical properties of WCFTs are revisited in the canonical and micro-canonical ensemble.

  • 9 December 2015, Judit Kovacs (Eotvos)

    Doublet-singlet model and unitarity

    Simplified models are useful tools to study the low energy extensions of the Standard Model. Here, we study a doublet-singlet fermionic extension, where new vector-like fermions couple to the weak gauge bosons and the Higgs via new Yukawa couplings. These allow for nontrivial mixing in the new sector, providing a stable, neutral dark matter candidate. We calculate the two particle scattering amplitudes in the model, impose the perturbative unitarity constraints and establish bounds on the Yukawa couplings.

  • 16 December 2015, Istvan Kaposvari (Eotvos)

    Scalar mass stability bound in a simple Yukawa-theory from renormalisation group equations slides

    Functional Renormalisation Group equations are constructed for a simple fermion-scalar Yukawa-model with discrete chiral symmetry, including also the effect of a nonzero composite fermion background beyond the conventional scalar condensate. Two approximate versions consistent with the scale dependent equations of motion are solved, taking into account also field renormalisation. The lower bound for the mass of the scalar field is determined requiring the stability of effective potential in the full momentum range, from the cutoff down to vanishing momentum. Close agreement is demonstrated with the results of previous studies done exclusively in presence of scalar condensate. A semiquantitative explanation is provided both for the negligible effect of the wave-function renormalisation and the narrow dispersion in the scalar mass bounds found from different approximation schemes.

  • 10 February 2016, Diego Correa (La Plata, Argentina)

    1-loop exponentiation for large rank Wilson loops slides

    In this talk I will describe Wilson loops in N=4 super Yang-Mills, for external particles in k-rank totally symmetric representations. I will argue that for large k the perturbative resummation of diagrams is dominated by ladder diagrams and simply given by the exponential of the 1-loop result. This will be verified -for a generic family of Wilson loops- in the strong coupling limit performing a classical D-brane computation and using the AdS/CFT correspondence.

  • 17 February 2016, Attila Pasztor (Wuppertal)

    QCD at small chemical potentials: the equation of state and fluctuations

    I will present some recent continuum extrapolated lattice results on QCD in the grand canonical ensemble. The chemical potentials and temperatures considered are relevant for the RHIC beam energy scan. The methods used are Taylor expansion near zero chemical potential and analytic continuation from an imaginary chemical potential. I will present comparisons with the hadron resonance gas model at low and with resummed perturbation theory at high temperatures.

  • 24 February 2016, Marton Lajer (Eotvos)

    Truncated Hilbert Space Approach for the 1+1D phi^4 Theory slides

    We used the massive analogue of the truncated conformal space approach to study the broken phase of the 1+1 dimensional scalar phi^4 model in finite volume, similarly to the work by S. Rychkov and L. Vitale. In our work, the finite size spectrum was determined numerically using an effective eigensolver routine, which was followed by a simple extrapolation in the cutoff energy. We analyzed both the periodic and antiperiodic sectors. The results were compared with semiclassical and Bethe-Yang results as well as perturbation theory. We obtained the coupling dependence of the infinite volume breather and kink masses for moderate couplings. The results fit well with semiclassics and perturbative estimations, and confirm the conjecture of Mussardo that at most two neutral excitations can exist in the spectrum. We believe that improving our method with the renormalization procedure of Rychkov et al. enables to measure further interesting quantities such as decay rates and the inelastic part of scattering matrices.

  • 2 March 2016, Gabor Cynolter MTA-ELTE)

    Diphoton excess, gauge invariance and perturbative unitarity

    I discuss some aspects of the recently reported excess in the diphoton resonance search by ATLAS and CMS. Assuming that the resonance is due to a new singlet (pseudo)scalar, 5-dimensional effective interactions are postulated. SU(2)xU(1) gauge invariance implies additional dim-5 interactions with the weak bosons leading to nontrivial constraints on the validity of the effective theory. The effective interactions can be generated at 1-loop by additional coloured and charged vector-like quarks, these favour narrow-width and are further constrained.

  • 9 March 2016, Gabor Takacs (BME)

    Particle Formation and Ordering in Strongly Correlated Fermionic Systems: Solving a Model of Quantum Chromodynamics slides

    We study a (1+1)-dimensional version of the famous Nambu-Jona-Lasinio model of Quantum Chromodynamics (QCD2) both at zero and finite matter density using non-perturbative techniques (non-Abelian bosonization and Truncated Conformal Space Approach). At zero density we describe a formation of fermion three-quark (nucleons and Delta-baryons) and boson (two-quark mesons, six-quark deuterons) bound states and also a formation of a topologically nontrivial phase. At finite matter density, the model has a rich phase diagram which includes phases with density wave and superfluid quasi-long-range (QLR) order and also a phase of a baryon Tomonaga-Luttinger liquid (strange metal). The QLR order results as a condensation of scalar mesons (the density wave) or six-quark bound states (deuterons).

  • 16 March 2016, Laszlo Hollo (Ecole Normale Superieure)

    On form factors of boundary changing operators slides

    We develop a form factor bootstrap program to determine the matrix elements of local, boundary condition changing operators. We propose axioms for these form factors and determine their solutions in the free boson and Lee-Yang models. The sudden change in the boundary condition, caused by an operator insertion, can be interpreted as a local quench and the form factors provide the overlap of any state before the quench with any outgoing state after the quench. http://arxiv.org/abs/1510.08232

  • 23 March 2016, Gabriella Pasztor (MTA-ELTE)

    Search for a New Heavy Boson in the di-photon channel (and elsewhere) at the LHC slides

    The ATLAS and CMS experiments observe a moderate excess of events in their search for new heavy bosons in the di-photon final state in the 2015 LHC data collected at a centre-of-mass energy of 13 TeV corresponding to about 3 fb^{-1} integrated luminosity per experiment. Is this a statistical fluctuation in the limited amount of 2015 data or maybe the first sign of New Physics? I will review the updated results on the di-photon search as well as the newly emerging results from other final states such a new particle could decay into.

  • 30 March 2016, Gyula Bencedi (MTA-Wigner)

    Multiplicity dependence of charged pion, kaon, and (anti)proton production at large transverse momentum in p-Pb collisions at 5.02 ATeV

    The discovery of fluid-like behaviour in small collision systems (like pp, pA) is one of the recent discoveries at the Large Hadron Collider (LHC). To understand the origin of the phenomenon several observables are being studied as a function of the event multiplicity. In particular, the measurement of identified particle production in a broad transverse momentum (pT) range provides valuable information since it is sensitive to flow-like effects and new hadronization mechanisms like recombination and jet quenching. In this talk I am going to present the recent results, arXiv:1601.03658v1 [nucl-ex], on the multiplicity dependence of charged pion, kaon and (anti)proton production in p-Pb collisions at 5.02 ATeV measured by the ALICE Collaboration at the LHC. The detailed discussion of the analysis to measure the pT spectra will be covered. Comparisons among pp, p-Pb and Pb-Pb collisions will be shown, in addition the nuclear modification factor for identified particles in non-single diffractive p--Pb collisions will be discussed as well.

  • 6 April 2016, Janos Balog (MTA-Wigner)

    Mass-coupling relation in quantum integrable models slides

    We determine exactly the mass-coupling relation in the simplest multi-scale quantum integrable model, the homogenous sine-Gordon model with two independent mass scales. We find a generalization of the ? sum rule Ward identity which enables one to derive a differential equation for the mass-coupling relation. The solution can be expressed in terms of hypergeometric functions.

  • 13 April 2016, Falk Bruckmann (Regensburg)

    Phase diagram of an asymptotically free sigma model through lattice dualization slides

    The 2d O(3) sigma model shares asymptotic freedom, mass generation and other nonperturbative features with 4d QCD. Likewise, a sign problem at nonzero chemical potential hampers numerical simulations of its thermodynamics. I demonstrate how mapping the corresponding lattice fields to dual degrees of freedom solves the sign problem. At finite volume and low temperatures this can be used to extract the phase shifts governing the particles' interaction. Moreover, I discuss the phase diagram of this model including a quantum phase transition and a comparison to an integrable model.

  • 20 April 2016, Zoltan Keresztes (Szeged)

    Gravitational, shear and matter waves in Kantowski-Sachs cosmologies slides

    A general treatment of vorticity-free, perfect fluid perturbations of Kantowski-Sachs models with a positive cosmological constant are considered within the framework of the 1+1+2 covariant decomposition of spacetime. The dynamics is encompassed in six evolution equations for six harmonic coefficients, describing gravito-magnetic, kinematic and matter perturbations, while a set of algebraic expressions determine the rest of the variables. The six equations further decouple into a set of four equations sourced by the perfect fluid, representing forced oscillations and two uncoupled damped oscillator equations. The two gravitational degrees of freedom are represented by pairs of gravito-magnetic perturbations. In contrast with the Friedmann case one of them is coupled to the matter density perturbations, becoming decoupled only in the geometrical optics limit. In this approximation, the even and odd tensorial perturbations of the Weyl tensor evolve as gravitational waves on the anisotropic Kantowski-Sachs background, while the modes describing the shear and the matter density gradient are out of phase dephased by Pi/2 and share the same speed of sound.

  • 27 April 2016, Nicolas Filipovic (Eotvos)

    Latest results on Quarkonium production in nuclear matter at the LHC slides

    In this talk I will review the latest experimental results on quarkonium production and nuclear modification at the LHC. I will introduce the basics of quarkonium modification in the Quark-Gluon Plasma (QGP), and present the current state-of-the-art measurements on charmonia and bottomonia. The emphasis will be put on the pp, pPb and PbPb data recorded by the CMS Collaboration during Run 1, with a look at the results from other experiments at LHC and RHIC.

  • 4 May 2016, Denes Sexty (Wuppertal)

    The complex Langevin equation and the sign problem in lattice QCD slides

    The Complex Langevin method is a proposal to solve sign problems by generating a positive measure ensemble on the complexified field manifold using analytical continuation. I report on recent developments such as gauge cooling and show simulation results in full QCD, and point out open questions and pitfalls of the method.

  • 11 May 2016, Antal Jakovac (Eotvos)

    Functional Renormalization Group at finite chemical potential slides

    In the talk I give a short overview about the Functional Renormalization Group (FRG) technique, the usually applied approximations and solution methods. Then I will discuss our recently developed approach to treat fermionic systems at small (zero) temperature and finite chemical potential on the example of a simple Yukawa-model. We determine the phase diagram on the coupling constant space, and discuss the role of the different approximation schemes (mean field, one-loop, FRG LPA). Finally I will mention some possible applications.

  • 18 May 2016, Szilveszter Harangozo (MTA-Wigner)

    A new Heavy-Ion Jet Interaction Generator, model updates and first results

    The popular HIJING event generator is redesigned to match the compatibility with ALIROOT and is rewritten to C++. We review here the design of the C++ interface and the connections to the PYTHIA event generator. With the development, new physics is introduced into the code, like the inclusion of new particle distribution functions, and the DGLAP evolution of the shadowing effect. We examine the first results of this updated model and discuss further update possibilities.

  • 25 May 2016, Walter Winter (DESY)

    High-energetic cosmic neutrinos and the test of fundamental physics slides

    The very recent discovery of a diffuse flux of cosmic neutrinos has introduced a new messenger of the high-energy universe in addition to photons at multiple wavelengths, cosmic rays, and now also gravitational waves. We discuss the possible origin of these neutrinos, and we illustrate how they could be used for tests of fundamental particle physics.

  • 15 June 2016, Balint Erdi (Eotvos)

    A sarkany-konfiguracio -- egy megoldas csodai slides

    A centralis konfiguraciok nagy szerepet jatszanak az n-test problemakkal kapcsolatos kutatasokban. Centralis konfiguraciok eseten az egyes tesekre hato eredo ero a rendszer tomegkozeppontjan megy at, es a testek onhasonlo konfiguracioju mozgast vegeznek. A haromtest-problema centralis konfiguracioi az Euler-Langrange-megoldasok. n>3-ra egyenlo tomegu szimmetrikus elrendezesek ismertek. Az eloadas roviden attekinti az eddigi legfontosabb eredmenyeket, es bemutat egy kozelmultban kapott analitikus megoldast a negytest-problema egy tengelyszimmetrikus esetere.

  • 22 June 2016, Attila Krasznahorkay (ATOMKI)

    On the track of the dark forces slides

    Electron-positron angular correlations were measured for the magnetic dipole 17.6 MeV and the 18.15 MeV transitions in 8Be. Significant enhancement relative to the internal pair creation was observed at large angles in the angular correlation for the 18.15 MeV transition with a confidence level of > 5sigma. This observation might indicate that, in an intermediate step, a neutral particle with a mass of 16.70 MeV/c^2 was created. In January we reported the above anomaly in Physical Review Letters, but at first, few took notice. That changed in April with a paper by Jonathan Feng, a theoretical particle physicist, who presented their work with the title of: ``Evidence for a Protophobic Fifth Force from 8Be Nuclear Transitions'', which was followed by an article in Nature with a title of: ``Has a Hungarian physics lab found a fifth force of nature?'' Such an article produced a boom in the media. The proposed boson has become lunch-table talk in physics departments far and wide, and plans are afoot for testing the idea. If the particle is confirmed, that would completely upend our understanding of the universe. I am going to show the reliability of the data, place such a particle into context with other experimental results and discuss the implications of the results.

  • 7 September 2016, Daniel Barna (Wigner)

    Magyar reszvetel a jovo 50-50 TeV-es gyorsitojanak fejleszteseben

    Az eloadasban szo lesz az FCC-rol (Future Circular Collider), a CERN kovetkezo generacios gyorsito terverol; arrol, hogy hogyan lehet megszabadulni az egyenkent 8.4 GJ energiat tarolo nyalaboktol (ami 23 darab 200 m hosszu, 150 km/h sebessegu TGV vonat mozgasi energiajanak felel meg); az LHC es az FCC nyalabtemetojerol; szupravezetokrol, szupravezeto magnesekrol es szupravezeto arnyekolasrol; specialis kicsatolo magnesekrol. Minderrol annak a Budapest-CERN kozos projektnek a kereteben fogok beszelni, ami iden indult, es a fenti problemakra keres megoldast, es fejleszt prototipusokat.

  • 21 September 2016, Matteo Giordano (Eotvos)

    Landau levels in QCD in an external magnetic field slides

    The effect of an external magnetic field on strongly interacting matter is relevant for important problems in particle physics and cosmology, such as heavy ion collisions, neutron stars, and the evolution of the early universe. In this talk I will first briefly review the current knowledge on this topic, as obtained by means of first-principles lattice numerical calculations. I will then discuss in detail the issue of Landau levels in QCD, showing preliminary numerical results obtained on the lattice. In particular, I will show that, after turning on the strong interactions, only the lowest Landau level remains of the whole Landau level structure. I will then discuss how much of the observed effects of a magnetic field can be explained in terms of the lowest Landau level. Our results can be used to test the validity of low-energy models of QCD that make use of the lowest-Landau-level approximation.

  • 28 September 2016, Gergely Fejos (Osaka University)

    Thermal properties and evolution of the axial anomaly for 2+1 flavors slides

    I will be talking about the thermal evolution of the axial anomaly of QCD in terms of effective theories with 2+1 flavors. It will be shown that mesonic fluctuations are of great importance from the point of view of the thermal behavior of the 't Hooft determinant term. Results indicate that fluctuations strengthen the axial anomaly at finite temperature and it does not vanish at the critical point. The phenomenon has been found to have significance in the thermal properties of the mesonic spectrum, especially concerning the eta - eta' system. Analysis of the spectrum and the anomaly in nuclear medium will also be discussed.

  • 5 October 2016, Sandor Katz (Eotvos)

    Axion cosmology from lattice QCD slides

    The strong CP problem of QCD can be solved via the Peccei-Quinn mechanism. The resulting pseudo-Goldstone boson, the axion is a natural candidate for dark matter. In order to quantitatively understand axion dark matter production two important QCD inputs are required: the equation of state and the topological susceptibility at high temperatures. We determine these quantities and use them to constrain the axion mass in different axion production scenarios.

  • 12 October 2016, Zoltan Kokenyesi (Eotvos)

    Chiral expansion and Macdonald deformation of two-dimensional Yang-Mills theory slides

    There is a conjecture that relates the partition function of a four-dimensional BPS black hole in Type IIA string theory compactified on a Calabi-Yau threefold with the A-model topological string amplitudes on the Calabi-Yau. The topological string amplitudes on special geometries reduce to a q-deformed version of two-dimensional U(N) Yang-Mills theory. We study the refined version of this duality which leads to a refinement of the two-dimensional Yang-Mills theory.

    We derive the analog of the large N Gross-Taylor holomorphic string expansion for the refinement ofq-deformed U(N) Yang-Mills theory on a compact oriented Riemann surface.The derivation combines Schur-Weyl duality for quantum groups with the Etingof-Kirillov theory of generalized quantum characters which are related to Macdonald polynomials. In the unrefined limit we reproduce the chiral expansion of q-deformed Yang-Mills theory derived by de Haro, Ramgoolam and Torrielli. In the classical limit q=1, the expansion defines a new beta-deformation of Hurwitz theory wherein the refined partition function is a generating function for certain parameterized Euler characters, which reduce in the unrefined limit to the orbifold Euler characteristics of Hurwitz spaces of holomorphic maps. We discuss the geometrical meaning of our expansions in relation to quantum spectral curves and beta-ensembles of matrix models arising in refined topological string theory.

  • 26 October 2016, Janos Polonyi (Strasbourg)

    Time scales of diffusion and decoherence slides

    A disszipativ es a dekoherenciahoz vezeto folyamatokat altalaban az utkozesek kovetesevel irjuk le (E. Joos, H. Zeh, Z. Phys. 59 223 (1985), B. Vacchini, K. Hornberg Phs. Rep. 478 71 (2009)). Ennel megbizhatobb, egy szisztematikus kozelitesen alapulo modszerrol, a tesztreszecske Schwinger--Keldysh effektiv Lagrange-fuggvenyenek kiszamolasarol lesz szo az eloadasban (Polonyi, arxiv.org/abs/1605.00834). Harom kis parameterben valo kifejtesre alapul a levezetes, melyek a kovetkezoek: a tesztreszecske-gaz kolcsonhatas erossege, a kolcsonhatas altal indukalt koordinata megvaltozas nagysaga es annak sebessege. Az utkozesi modell alapjan a dekoherenciat sok nagysagrenddel gyorsabbnak kepzelik mint a disszipacios folyamatokat. Ugyan ennek az elvarasnak az alapjaul szolgalo egyenletekhez hasonlora vezet az uj modszer, azonban az is kiderul, hogy az emlitett kovetkezmenyre az egyenleteknek alkalmazhatosagi tartomanyan kivuli hasznalata vezet el. Ez az utkozesi modellben a tobbszoros utkozesek tartomanyanak felel meg. Az egyenletek figyelmesebb hasznalata alapjan a dekoherencia nem adodik gyorsabbnak a disszipacional, inkabb egymashoz kozel marad a ket idoskala. Harom kulonbozo dekoherencia fogalmat lehet az uj levezetes gondolatmenete alapjan megkulonboztetni es az egzaktul megoldhato harmonikus rendszerekben a "valodi" dekoherencia az ido dupla exponencialis fuggese alapjan all be. Ez a Schwinger--Keldysh-leiras egy figyelmre melto tulajdonsaganak egyszeru kovetkezmenye, nevezetesen annak, hogy nyilt, disszipativ rendszerekben az ido ellentetes iranyban folyik a megfigyelheto mennyisegekben mint a kvantum fluktuaciokban. Tehat vegul is nagyon gyorsan all be a dekoherencia, sokkal gyorsabban mint barmely mas fizikai folyamat csak epp nem vilagos az aszimptotikus allapot eleresenek a modja a kolcsonhato rendszerekben, mert annak leirasara az alkalmazott kifejtesek kereten belul egyenlore nem latszik lehetoseg.

  • 2 November 2016, Istvan Szecsenyi (Durham, BME)

    TTbar-deformed 2D Quantum Field Theories slides

    It was noticed many years ago, in the framework of massless RG flows, that the irrelevant composite operator TTbar, built with the components of the energy-momentum tensor, enjoys very special properties in 2D quantum field theories, and can be regarded as a peculiar kind of integrable perturbation. Novel interesting features of this operator have recently emerged from the study of effective string theory models. In this talk, we focus on further properties of this distinguished perturbation. We discuss how it affects the energy levels and one-point functions of a general 2D QFT in finite volume through a surprising relation with a simple hydrodynamic equation. We argue that, at the classical level, the deformation naturally maps the action of N massless free bosons into the Nambu-Goto action in static gauge, in N+2 target space dimensions, and we briefly discuss a possible interpretation of this result in the context of effective string models.

  • 16 November 2016, Arpad Hegedus (Wigner)

    Numerical solution and strong coupling results in the spectral problem of planar AdS/CFT correspondence slides

    Maldacena's famous AdS/CFT correspondence states that type IIB string theory on AdS5 x S5 background is equivalent to maximally supersymmetric Yang-Mills theory with SU(N) gauge group. In the large N (planar) limit integrability was discovered on both sides of the correspondence, which makes it possible to get exact results in the planar limit. In this talk we use integrability to compute numerically the anomalous dimensions for twist-2 operators in the super-Yang-Mills theory. Numerical data allowed us to get the coefficients of the strong coupling series expansion of the anomalous dimensions with high precision and to compare them with earlier proposals.

  • 23 November 2016, Monika Kofarago (Wigner)

    Characterization of the near-side jet-peak in Pb- Pb collisions at sqrt(s_NN) = 2.76 TeV at ALICE slides

    By studying jets which propagate through the medium produced in heavy-ion collisions, one can get insight to the properties of the quark-gluon plasma. At low p_T the reconstruction of jets is difficult over the large fluctuating background, and instead two-particle angular correlation measurements can be used to study the  interplay of jets with the produced medium. In these measurements jets manifest themselves as a near-side peak, and the interactions would result in a centrality dependent modification of this peak. I will present the results obtained by the ALICE detector in pp and Pb--Pb collisions at 2.76 TeV, which show an asymmetric broadening of the near-side peak in Pb--Pb collisions towards central events at low p_T. The broadening is more pronounced in the Delta eta direction, and a novel feature is also observed at low p_T in central collisions: the peak shape depart from a Gaussian and a depletion around (Delta phi,Delta eta) = (0,0) develops. The data is compared to AMPT simulations to study the influence of longitudinal, radial and elliptic flow, and the studies suggest that the interplay of jets with radial and longitudinal flow play a key role in the development of the observed effects.

  • 30 November 2016, Bence Kocsis (Eotvos)

    The dynamical origin of black hole mergers

    With the detections of the gravitational waves emitted during black hole mergers, LIGO has recently opened the field of gravitational wave astrophysics. In this talk I will discuss some of the astrophysical processes that may be responsible for the observed events. Although less than 0.5% of the stellar mass is in dense stellar systems, I will argue that a large fraction of the black hole mergers may originate in these environments due to gravitational bremsstrahlung and multibody interactions. Accretion disks in active galactic nuclei may also facilitate black hole mergers. Finally, if primordial black holes constitute a fraction of dark matter, gravitational waves may shed light on its composition. I will discuss predictions on the event rate distribution that may be used to disentangle these astrophysical processes to understand the origin of the observed gravitational wave events.

  • 7 December 2016, Kentaroh Yoshida (Kyoto University)

    Recent progress on Yang-Baxter deformations of type IIB superstring slides

    It is well-known that type IIB superstring theory on the AdS_5 x S^5 background is classically integrable. Recently, integrable deformations of this system have been studied very actively by adopting a systematic way called the Yang-Baxter deformation. With this method, integrable deformations are specified by classical r-matrices satisfying the classical Yang-Baxter equations. In this talk, I will give a review on recent progress on this issue. Classical r-matrices in a certain class lead to well-known examples of type IIB supergravity solutions including the Lunin-Maldacena backgrounds (dual for beta deformations of the N=4 super Yang-Mills theory), the Maldacena-Russo backgrounds (dual for non-commutative gauge theories) and Schroedinger spacetimes (dual for non-relativistic conformal field theories). In general, however, the resulting deformed backgrounds are not solutions of the standard type IIB supergravity, but of the generalized one. Finally, I will describe the relation between Yang-Baxter deformations and non-abelian T-dualities.

  • 14 December 2016, Csaba Torok (Eotvos)

    The sign problem in the O(3) nonlinear sigma model at finite chemical potential

    I am going to talk about the 1+1 dimensional nonlinear O(3) model at finite chemical potential and compare different methods to overcome the sign problem: the complex Langevin algorithm, the density of states method and the worm algorithm. In the latter, the sign problem is totally eliminated. We determine the range of parameters, where complex Langevin produces correct results and study whether taking the continuum limit allows the exploration of the full phase diagram of the model.

  • 8 February 2017, Arpad Lukacs (Wigner)

    Stabilisation of semilocal strings by dark scalar condensates slides

    Semilocal and electroweak strings are well-known to be unstable against unwinding by the condensation of the second Higgs component in their cores. A large class of current models of dark matter contains dark scalar fields coupled to the Higgs sector of the Standard Model (Higgs portal) and/or dark U(1) gauge fields. It is shown, that Higgs-portal-type couplings and a gauge kinetic mixing term of the dark U(1) gauge field have a significant stabilising effect on semilocal strings in the "visible" sector. Preprint

  • 15 February 2017, Marton Kormos (BME)

    Quantum quenches in the non-integrable Ising model: Hamiltonian truncation method and dynamical confinement slides

    In contrast to lattice systems where powerful numerical techniques are available to study the out of equilibrium dynamics, the non-equilibrium behaviour of continuum systems is much harder to simulate. In the first part of my talk I will demonstrate that Hamiltonian truncation methods can be efficiently applied to this problem, by studying the quantum quench dynamics of the 1+1 dimensional Ising field theory using a truncated free fermionic space approach. After benchmarking the method with integrable quenches corresponding to changing the mass in a free Majorana fermion field theory, I will study the effect of an integrability breaking perturbation by the longitudinal magnetic field. In both the ferromagnetic and paramagnetic phases of the model we find persistent oscillations with frequencies set by the low-lying particle excitations even for moderate size quenches. In the ferromagnetic phase these particles are the various non-perturbative confined bound states of the domain wall excitations. Turning to the same quench in the Ising spin chain I will show that the interplay between the quantum quench and confinement results in a strong suppression of the light cone propagation of correlations and entanglement.

  • 22 February 2017, Giuseppe Bevilacqua (MTA-DE Particle Physics Research Group, Debrecen)

    Off-shell effects in top pair production with jet activity at the LHC slides

    Investigating the dynamics of top quark production and decay is an important part of the LHC physics program. In particular, a precise determination of the cross section of top-pair production (and its jet activity) is crucial for a variety of applications. Besides representing a background for Higgs boson analyses and for several searches of physics beyond the Standard Model, it provides competitive methods for extracting the value of the top quark mass with high precision. This is only possible in synergy with the most accurate state-of-the-art description of the process. Given the extremely short lifetime of the top quark, any realistic simulation of tt+jets cannot prescind from a genuine multi-particle calculation, which puts serious challenges when going beyond the leading order in perturbation theory. For this reason theoretical predictions are often restricted to on-shell top quarks, and decays are treated in the Narrow Width Approximation under the assumption that the off-shell contributions are suppressed. While this approach is adequate for many analyses, there are issues that cannot be tackled without a complete calculation. I will discuss some examples where the impact of top quark off-shell effects is phenomenologically relevant. Then, motivated by these arguments, I will show recent progress in the calculation of complete off-shell effects to tt+jet production at NLO QCD accuracy.

  • 8 March 2017, Yunfeng Jiang (ETH Zurich)

    Integrable line defects and entanglement entropy slides

    In this talk, I will discuss entanglement entropy of integrable field theories in 1+1 dimensions in the presence of line defects which preserves integrability. For interacting field theories, integrable defects are topological while for free theories the defects can be non-topological. Using the replica trick and the form factor bootstrap method of integrable field theories, I will show that topological defects do not modify the UV behavior of the bulk entanglement entropy but lead to different corrections in the IR limit. On the contrary, non-topological defects modify both the UV and IR behavior of the bulk entanglement entropy.

  • 22 March 2017, Gergely Marko (Eotvos)

    2PI solutions of the phi^4 model across the complex plane slides

    Solutions of the phi^4 model in the two-particle irreducible (2PI) formalism along with other methods involving a self-consistent propagator are mainly accessible in Euclidean space. Therefore to obtain the spectral function, or to find complex poles of resonances analytic continuation is needed. A method to analytically continue numerically known propagators is to construct their Pade approximants. In the case of two-loop 2PI we solved the equations both in Euclidean and directly in Minkowski space which allowed us to test the quality of this type of analytic continuation. Based on the encouraging test results, using the same method we analyzed Euclidean data from our previous works, yielding spectral functions and physical pole masses.

  • 29 March 2017, Gyula Fodor (MTA-Wigner)

    Self trapped gravitational waves (geons) with anti-de Sitter asymptotics slides

    Geons are localized horizonless objects formed by gravitational waves held together by the gravitational attraction of their own field energy. If there is a negative cosmological constant, the spacetime of geons asymptotically approaches the anti-de Sitter (AdS) metric. AdS geons are time-periodic regular localized vacuum solutions without any radiation loss at infinity. A perturbative construction in terms of an amplitude parameter shows that there are one-parameter families of AdS geon solutions emerging from combinations of same-frequency linear modes of the system. Numerical results will also be presented about higher amplitude helically symmetric rotating AdS geon solutions, which were obtained by a spectral numerical code.

  • 5 April 2017, Istvan Kaposvari (ELTE)

    Pseudo-Goldstone excitations in chiral Yukawa-theories with quadratic explicit symmetry breaking slides

    The symmetry breakdown pattern is studied in models containing one fermion flavor multiplet and a multicomponent scalar field, supplemented with a chiral Yukawa-interaction, and in presence of an explicit symmetry breaking source quadratic in the scalar field. In a detailed investigation of the model with U_L(1) x U_R(1) chiral symmetry it is shown that by diminishing the strength of quadratic explicit symmetry breaking one can still keep stable the mass ratio of the fermionic and the pseudo-Goldstone excitation. At the same time the mass ratio of the two bosonic excitations appears to approach a limiting value depending only on the infrared value of the first ratio, but not on the microscopic (ultraviolet) coupling values. The observations receive a general interpretation by the existence of an ultraviolet fixed point located in the symmetric phase. Understanding the general conditions for its existence allows the construction of a similar theory with U_L(2) x U_R(2) chiral symmetry. All results of the present investigation were obtained with non-perturbative Functional Renormalisation Group technique.

  • 19 April 2017, Peter Vecsernyes (Wigner-MTA)

    A toy model of selective measurement in quantum mechanics slides

    The non-selective and selective measurements of a self-adjoint observable A in QM are interpreted as `jumps' of the state of the measured system into a decohered or pure state characterized by the spectral projections of A. However, one may try to describe the measurement results as asymptotic states of a dynamical process, where the non-unitarity of time evolution arises as an effective description of the interaction with the measuring apparatus. The dynamics we present is a two-step dynamics: the first step is the non-selective measurement or decoherence, which is known to be described by the linear Lindblad equation, where the generator of the time evolution is the generator of a semigroup of unit preserving completely positive maps. The second step is a process from the resulted decohered state to a pure state, which is described by an effective non-linear toy model dynamics that have the pure states as fixed points, and the emergent probabilities arise as the relative volumes of their attractor regions.

  • 26 April 2017, Tamas Vertesi (ATOMKI)

    Bell nonlocality from bound entanglement

    In 1999, Asher Peres conjectured that bound entanglement can never lead to Bell nonlocality. Recently this conjecture has been proven to be false, by identifying a 3x3 bound entangled state that violates a bipartite Bell inequality (Vertesi and Brunner, 2014). In this talk, we discuss implications of this result to the relation between different facets of quantum entanglement. Also, possible extensions of the problem to higher dimensional and multipartite states are presented.

  • 3 May 2017, Yohai Meiron (Eotvos)

    Detecting triple systems with gravitational wave observations slides

    The Laser Interferometer Gravitational Wave Observatory (LIGO) has recently discovered gravitational waves (GWs) emitted by merging black hole binaries. We examine whether future GW detections may identify triple companions of merging binaries. Such a triple companion causes variations in the GW signal due to the varying path length along the line of sight during the orbit around the center of mass (Doppler shift). Other effects such as relativistic beaming, gravitational redshift, and Shapiro may also distort the waveform. We find that the prospects for detecting the triple companion are the highest for low-mass compact object binaries which spend the longest time in the LIGO frequency band. In particular, for merging neutron star binaries, LIGO may detect a white dwarf or M-dwarf perturber at signal to noise ratio of 8, if it is within 0.4 solar radius distance from the binary and the system is within a distance of 100 Mpc. Stellar mass (supermassive) black hole perturbers may be detected at a factor 5x (1000x) larger separations. Such pertubers in orbit around the merging binary emit GWs at frequencies above 1 mHz detectable by the Laser Interferometer Space Antenna (LISA) in coincidence.

  • 17 May 2017, Gabor Papp (Eotvos)

    Portfolio Optimization with Statistical Physics slides

    In this talk I present the financial optimization problem, and reformulate it in the language of statistical physics. The randomness of price fluctuation may be treated with the replica trick, allowing us to access the free energy of the system. The analytical and numerical results are compared, allowing us to make estimation on the precision of empirically deduced optimal portfolio. We also study the effect of regularization on the estimate. The results are also of relevance to any multichannel measurement experimental evaluation and to Deep Learning regularization.

  • 11 October 2017, Matteo Giordano (Eotvos)

    Quantum gravity on the lattice: a new look at an old problem slides

    The formulation of general relativity as a (kind of) gauge theory has been the starting point of several nonperturbative approaches to quantum gravity. In this talk I will briefly introduce the gauge formulation of gravity and discuss related attempts at quantisation on the lattice, focussing on the difficulties of this approach. I will then show some preliminary results of our numerical studies, and discuss a few yet unexplored directions.

  • 18 October 2017, Haryanto Siahaan (MTA-Wigner)

    Some aspects of magnetized black holes slides

    In the last couple of years, there has been a growing interest in the studies of black holes interacting with external magnetic fields. One of the reasons is that astronomers found some evidence of strong magnetic fields in the centers of galaxies, where normally supermassive black holes sit. When the external magnetic field cannot be treated as some perturbations, the exact solutions by Ernst in Einstein-Maxwell theory can be employed to model a magnetized black hole. The solution is obtained by applying a Harrison-like transformation to a known unmagnetized one, which is also in the Einstein-Maxwell theory. However, the resulting magnetized spacetime has no asymptotic flatness anymore. Nevertheless, some interesting questions can still be addressed to the magnetized black holes in Einstein-Maxwell theory, which will be discussed in this talk. One of the questions is whether the conjectured Kerr/CFT correspondence still holds in the case of rotating black holes immersed in a strong magnetic field. The Kerr/CFT correspondence states that the physics of four dimensional rotating black holes is dual to a two dimensional conformal field theory (2d CFT). Some evidences in supporting this conjecture are the ability of entropy and scattering formulas in 2d CFT to recover the Bekenstein-Hawking entropy and scattering process calculation in the black hole background. Another question is about the possibility of destroying a magnetized black hole by using a test particle. It can be shown that a near extremal black hole can be turned into a naked singularity if the black hole captures a classical test particle released from far away. One may wonder how the presence of external magnetic field may contribute to the possibility of destroying a black hole immersed in this field.

  • 25 October 2017, Adam Kardos (Debrecen)

    NNLO QCD calculations at work: determining the strong coupling in electron-positron annihilation slides

    The strong coupling is one fundamental parameter of the standard model. Its most precise determination is demanded. One way to obtain it is from physical observables defined in electron-positron collisions. The strong coupling is extracted using a fitting procedure over a range of the observable. In order to minimize theoretical uncertainties the most precise fixed-order calculation has to be used in perturbation theory which is matched to another one where contributions coming from all orders are summed up. In my talk I present the determination of strong coupling in electron-positron annihilation using two-particle correlations as the physical observable.

  • 2 November 2017, Janos Polonyi (Strasbourg)

    Electrodynamics near the classical electron radius slides

    The absence of non-perturbative, relativistic regulators in quantum field theory has troubled me since a long time. This problem is discussed within the context of the last open chapter of classical electrodynamics, the radiation reaction force of a point charge. The mysterious conflict with causality and stability turns out to be the result on the one hand of the lack of relativistic regulator and the other hand of a naive, pre-renormalization group way of arguing. A more careful calculation reproduces the Abraham-Lorentz force without instability as a saddle point effect of QED. There are two interesting lessons to be learned here: One is that we have no general argument about the stability of a relativistic field theory of point particles, in particular the stability of electrodynamics can be established numerically only. The other is that the perturbative classical effective theories contain loop diagrams making regularization and renormalization necessary already at the level of the classical saddle point physics.

  • 8 November 2017, Lorinc Szikszai (Eotvos)

    Lattice gauge theory with a topological action slides

    We investigate a topological lattice action in SU(2) gauge theory. This action only contains a sharp cutoff in field space and does not give rise to classical field equations. These kinds of actions were investigated in sigma models before and shown to lead to the correct quantum continuum limit. We investigate both finite and zero temperature observables and the running coupling. In all cases we find the same continuum result as with the usual lattice actions. Our study shows the robustness of universality.

  • 22 November 2017, Zoltan Zimboras (MTA-Wigner)

    Quantum information theory concepts in high energy physics

  • 29 November 2017, Tamas Biro (MTA-Wigner)

    Entropy Production During Hadronization of a Quark-Gluon Plasma slides

    We revisit some physical pictures for the hadronization of quark-gluon plasma, concentrating on the problem of entropy production during processes where the number of degrees of freedom is seemingly reduced due to color confinement. Based on observations on Regge trajectories we propose not having an infinite tower of hadronic resonances. We discuss possible entropy production mechanisms far from equilibrium in terms of stochastic dynamics.

  • 13 December 2017, Antal Jakovac (Eotvos)

    Quantum Measurement Theory from the Functional Renormalization Group Perspective slides

    In the talk the quantum measurement problem is discussed from a novel point of view. An effective model is proposed for the measurement devices, concentrating only its relevant degrees of freedom. As it will be argued, the most simple measurement device is realized by spontaneous symmetry breaking (SSB), and so the effective model of quantum measurements can be thought as a generalization of SSB. In the talk the SSB is treated in a purely quantum way with the help of functional renormalization group, which reveals how the fixed point structure is connected to the quantum-classical crossover. At the end well known experiments and paradoxes (Stern-Gerlach experiment, uranium decay, Schrödinger's cat) are discussed from the point of view of this new interpretation.

  • 21 February 2018, Andras Laszlo (Wigner-MTA)

    Quantification of the GR contribution to the muon g-2 measurement slides

    Recently, Morishima, Futamase and Shimizu published a series of manuscripts, putting forward arguments, based on a post-Newtonian approximative calculation, that there can be a sizable general relativistic (GR) correction in the experimental determination of the muon magnetic moment, i.e., in muon g-2 experiments. In response, other authors argued that the effect must be much smaller than claimed. Further authors argued that the effect exactly cancels. All this indicates that it is difficult to estimate from first principles the influence of GR corrections in the problem of spin propagation. Therefore, in this paper we present a full general relativistic calculation in order to quantify this effect. The used methodology is the purely differential geometrical tool of Fermi-Walker transport over a Schwarzschild background. This is compared to the Minkowski limit in order to quantify the GR corrections. The correction turns out to be of first order in terms of the Schwarzschild radius, and is increasing with particle velocity, and thus is sizable for ultrarelativistic particles. The calculated effect can be basically attributed to the contribution of general relativity to the Thomas precession, which appears since the muons are forced to move on a non-geodesic trajectory. Our calculation, however, does not include the Larmor precession, which is present in the real experiment, only the Thomas precession of the gyroscopic motion which is of purely kinematic origin. Taking this into account, the presented calculation, showing a 1ppm relative systematic error, can only be regarded as a preliminary estimate. Preprint: 1803.01395.

  • 28 February 2018, Tamas Gombor (ELTE)

    New boundary transfer matrices for classical sigma models slides

    The 2d principal models without boundaries have symmetry group GxG. The possible classical symmetries with integrable boundaries found so far are HxH or G_D where H is a subgroup of G for which G/H is symmetric space and G_D is the diagonal subgroup of GxG. A common property of these known boundary conditions is that they do not contain any free parameters. We have found new integrable boundary conditions for which the remaining symmetry groups are either GxH or HxG and they contain one free parameter. The related boundary transfer matrices are also described.

  • 7 March 2018, Miklos Werner (BME)

    TEBD simulation of quantum quenches in the S=1 Heisenberg chain: numerical test of the semiclassical approximation slides

    We investigate quantum quenches in the antiferromagnetic S=1 Heisenberg chain. Due to the gap in the excitation spectrum, after a small quench, the initial state is supposed to be a dilute gas of magnons (with spin S=1). An effective approach is then the so called semi-classical description, where we describe the system as a classical gas of quasiparticles that collide totally reflectively with each other. In our work we make an attempt to test the predictions of the semi-classical description, by comparing them with large scale TEBD simulations. In our calculations we exploit the SU(2) symmetry of the model, that radically speeds up the calculations and provides an easy way to extract the total spin of the states. We find that the half-chain spin fluctuations at short times are accurately described by semi-classics. However, at longer times the effect of fast (non reflected) quasiparticles make the semi-classical description untenable.

  • 14 March 2018, Daniel Berenyi (Wigner-MTA)

    Chiral Magnetic Effect with Wigner Functions slides

    The Chiral Magnetic Effect is a chiral anomaly effect that manifests in an electric current parallel to an external magnetic field. It is expected to form in non-central heavy ion collisions, where the moving highly charged nuclei induce the external magnetic field orthogonal to the reaction plane. During the collision left and right handed quarks interact with the QCD gauge fields resulting in chirality changes, charge separation and finally, electric current. Usually, the effect is calculated on the lattice, but here we describe an alternate formulation with relativistic Wigner functions. With suitable transformations, the external magnetic and QCD fields can be transcribed into a QED formulation and the equation of motion for the Wigner function can be solved. In this talk I summarize the Wigner function formalism, the formation of the anomalous current and the results obtained by inspecting the time evolution of the system. https://arxiv.org/abs/1707.03621

  • 28 March 2018, Rajan Gupta (Los Alamos National Lab, USA)

    Precision calculations of nucleon structure using lattice QCD

    I will provide high precision results on matrix elements of quark bilinear operators between nucleon states using lattice QCD. From these, we extract a number of exciting quantities, at the intersection of nuclear and particle physics. We show that the axial charge g_A, a fundamental parameter encapsulating the weak interaction of nucleons, is calculated with a few percent accuracy. Results for the scalar and tensor charges, g_S and g_T, which combined with precision neutron decay distribution probe novel scalar and tensor interactions at the TeV scale. Vector form factors are probed in electron scattering, while axial vector form factors are used in the calculation of the cross-section of neutrinos on nuclear targets. These energy dependent cross-sections are needed to determine the neutrino flux, an important systematic in neutrino oscillation experiments.

  • 4 April 2018, Dezso Horvath (Wigner-MTA)

    Anomalous magnetic moment of the muon slides

    The muon is 200 times heavier brother of the electron. As it is a heavy lepton with relatively long (2.2 microsec) lifetime it is the most penetrative charged particle and so the favourite messenger of new physical phenomena of particle physics. The present lecture will be devoted to the anomalous magnetic moment of the muon: its measurement and the deviation between the measured and calculated values which could be a sign of physics beyond the standard model.

  • 11 April 2018, Marton Lajer (Eotvos-Wigner-MTA)

    Luscher corrections for non-diagonal form factors in integrable QFTs slides

    I will outline a framework that provides direct access both to the excited states' finite volume energy levels and non-diagonal form factors in integrable QFTs. The idea is to expand and analytically continue the Euclidean torus two-point function in the limit when the major radius is sent to infinity. We obtained the first Luscher correction for a one-particle form factor of local operators in any integrable theory involving only a single massive excitation. We then applied the result to the Sinh-Gordon model and the form factor of the field operator, and expanded the same quantity in the coupling constant using Hamiltonian perturbation theory. Comparing the results in the regime where the two expansions overlap, we found complete agreement.

  • 13 June 2018, Alessandro Sfondrini (ETH Zurich)

    Integrable spin chain for stringy Wess-Zumino-Witten models

    For the first time we reveal the integrable structure of the CFT2 describing superstrings on AdS3xS3xT4 with pure NS-NS background fluxes. The Wess-Zumino-Witten spectrum is reproduced by a remarkably simple integrable spin chain with exactly solvable Bethe equations. This paves the way to establishing a firm contact between integrability and CFT2 techniques. Based on arXiv:1806.00422, arXiv:1804.01998.

  • 12 September 2018, Zsolt Frei (Eotvos)

    The road to the detection of gravitational waves, and ELTE's contribution to the quest

    I will briefly summarise what we all know by now about gravitational waves (GW) as a prediction of general relativity, the history of searching for the waves, and some technical details of the Laser Interferometer Gravitational-wave Observatory (LIGO), where the group I formed participated since 2007.

    I will tell you about our contribution to the data search: we have been an active member of the so-called "burst" group, where we are searching for transient-type signals in the noisy data stream of the detector. We have came up with two new search methods, the "Locust" and "Hough" algorithms. We also contributed to the experiment by developing, making and installing infrasound detectors at both the Hanford and Livingston sites. These detectors are increasingly important to measure the srength of gravity gradient noise, so I will spend some time to elaborate on this topic. Lately, we are also contributing to the identification of possible electromagnetic (EM) counterparts of the newly detected GW sources: binary neutron stars. We have developed a new galaxy catalog for LIGO, containing 2.5 million galaxies (compared to the 50.000 galaxies in the catalog LIGO used before). Some of our partners actually found the EM counterparts of the 2018 August event using our data.

    I will conclude with our current work and plans for the future: launching 9 small satellites to low-Earth orbit within the next 5 years to detect gamma-rays originating from binary neutron star merges and using these detections to precisely and promptly locate (triangulate) the position of the sources of the emerging GWs on the sky for subsequent EM observations.

  • 19 September 2018, Ankita Mehta (Eotvos)

    Study of double-parton scattering processes using same-sign WW events at the CMS experiment slides

    Double-parton scattering (DPS) processes include the simultaneous occurrence of two distinct hard parton-parton interactions within in a single proton-proton collision. These interesting physics processes could provide valuable information on the distribution of partons inside the proton in the transverse direction and act as a background for SM and new physics searches at the LHC. This presentation is based on the results obtained from the first search for same-sign WW production via DPS processes, based on proton-proton collision data at a center-of-mass energy of 8 TeV. The decay of two W bosons is considered in dimuon and electron-muon final states. A multivariate analysis is used to discriminate the single from different background processes. Obtained results on the production cross section for same-sign WW via DPS and effective cross section parameter for DPS processes are compared with existing measurements and predictions from MC event generators.

  • 26 September 2018, Attila Pasztor (Eotvos)

    QCD thermodynamics at finite density from imaginary chemical potential slides

    I will present a mini-review of some recent lattice QCD results on the bulk thermodynamic properties of QCD matter at finite temperature and small nonzero chemical potential. I will mostly focus on observables relevant for the RHIC Beam Energy Scan.

  • 3 October 2018, Keming Shen (Wigner-MTA)

    Hadronization within Non-Extensive Approaches slides

    However Tsallis-like distributions describe well the momentum spectra measured in high-energy nuclear collisions, to find the microscopical origin of the non-extensive behavior is not straightforward. Our aim is to explore source of this distribution from the first principles.

    We investigated the transverse momentum distributions of various identified charged particles in high energy relativistic heavy ion collisions. I studies the interpretations of these spectra within the non-extensive approaches in details. Results on best-fits show that the mass scaling behaves more explicit with heavier produced hadrons in both pp and heavy ion collisions. In this talk I'll present my recent investigations and new results on mass-scaling and on specific distribution-types.

  • 10 October 2018, Zoltan Kokenyesi (Eotvos)

    Topological string theory and generalized geometry slides

    Generalized geometry is a natural framework for describing geometric and non-geometric flux backgrounds in string compactifications. We study the A- and B-models of topological string theory and construct a membrane sigma-model based on a generalized complex structure, which reduces to the A- or B-models on the boundary in different gauges. Our construction allows the introduction of geometric and non-geometric fluxes as well as an S-duality at the level of the membrane sigma-model based on the generalized complex structure, and we interpret it as topological S-duality, which exchanges the A- and B-models. As an outlook we also discuss the relation of membrane sigma-models in topological M-theory to generalized geometry of M-theory.

  • 17 October 2018, Zoltan Trocsanyi (Eotvos)

    On the origin of neutrino masses

    We consider an anomaly free extension of the standard model gauge group G_SM by an abelian group to G_SM x U(1)_Z. The condition of anomaly cancellation is known to fix the Z-charges of the particles, but two. We fix one remaining charge by requiring that the masses of the left handed neutrinos are generated by a mixing with right-handed neutrinos that obtain their masses through interaction with a new scalar field whose vacuum is broken spontaneously. We discuss some of the possible consequences of the model and ways of constraining the parameter space.

  • 24 October 2018, Zoltan Kunszt (ETH Zurich)

    Feynman 100, Neutrino '72 Balatonfured slides

    The talk will shortly overview Feynman's unique, ingenious, inspiring scientific achievements as well as his teaching and popular lectures. Feynman's talk at Balatonfuered will be put in historic perspective in conjunction with the discovery of the QCD improved parton model.

  • 25 October 2018, Akio Tomiya (RIKEN)

    Phase structure of three flavor QCD in external magnetic fields using HISQ actions slides

    We study the phase structure of QCD with three degenerate flavors in external magnetic fields using HISQ actions. The simulations are performed on 16^3. In order to investigate the quark mass dependence of the QCD transition we vary the values of pion masses from m=320 MeV to 80 MeV in the continuum limit. We found no indication of a first order phase transition in the current window of quark masses and external magnetic fields. Unlike to the case with standard staggered fermions inverse magnetic catalysis is always observed above the critical temperature. The microscopic origin of this phenomena as well as the volume effects are further discussed by looking into the Dirac eigenvalue spectrum.

  • 31 October 2018, Dezso Horvath (Wigner-MTA, Atomki Debrecen)

    Recent results in Higgs studies and BSM searches at the LHC slides

    The almost half-century old theory of particle physics, the standard model (SM) seems to describe most of the experimental data very well. All of its elementary particles were identified and studied, and the discovery of the Higgs boson by ATLAS and CMS at the LHC with the mass m(H) = 125.09 +/- 0.21 (stat.) +/- 0.11 (syst.) GeV proved the validity of the Brout-Englert-Higgs mechanism of spontaneous symmetry breaking. In spite of the general quantitative agreement of its predictions with experiment the SM has serious theoretical shortcomings. It cannot account for neutrino oscillations, cannot solve the hierarchy problem (the unnaturally high corrections to the mass of the Higgs boson), there is no place in it for the particles of dark matter, and it cannot explain the lack of antimatter galaxies in the universe. Its gauge couplings are converging but not to the same point at high energies and it cannot include gravity as a gauge interaction. Most of these problems are solved within the frameworks of SM extensions, the most popular of them being supersymmetry. The latter predicts several deviations from the SM, especially in the Higgs sector, where it expects 5 Higgs bosons, three neutral and two charged ones.

    Studying the observed Higgs boson may uncover new physics beyond the SM, and thus it is one of the most important programs for the experiments of the Large Hadron Collider. We summarize the activity of CMS and also ATLAS to measure the mass and couplings of the 125 GeV Higgs boson, its decay properties as compared to the SM predictions, and also attempts to check for other Higgs bosons at different masses. Thus far all data collected by ATLAS and CMS agree with the SM, no deviation is found. Great effort is invested by both experiments to study extensions of the standard model and possibly uncover physics beyond it. We shall describe the history of an aborted discovery: a new boson at 750 GeV. Thus the question what new physics is beyond the SM is open yet.

    The talk is based on a plenary given on behalf of CMS at the QCD at LHC 2018 Workshop, 27-31 August 2018, Dresden (Germany).

  • 7 November 2018, Vladimir Korobov (Dubna)

    Precision theory for hydrogen molecular ions

    At present theoretical prediction for the spin-averaged frequency of ro-vibrational transitions in the hydrogen molecular ions (HMI) has reached a relative precision of ~ 7.5 x 10^(-12) . On the other hand, recent experiment on pure rotational transition in HD+ has demonstrated the power of the Lamb-Dicke regime for precision spectroscopy of the HMI with strong potentiality in the nearest future to achieve a ppt level of spectroscopic accuracy.

    The Rydberg constant as it is determined in the CODATA14 adjustment of the fundamental constants has the relative uncertainty 5.9 x 10^(-12). At the same time the two new experiments on spectroscopy of hydrogen atom performed at LKB, Paris, and MPQ, Munich, disagree in measuring the Rydberg constant by more than 3-sigma!

    In our presentation we want to outline the way how the high precision results for the hydrogen molecular ions may be achieved with the help of the effective field theory --- the Nonrelativistic QED. At the very end of our talk we intend to discuss the problems, which are to be solved in order to improve (at least threefold) theoretical predictions. That will bring our theory to the level of accuracy which is better than for the present CODATA14 value of the Rydberg constant. And, we hope, that this will help to resolve the discrepancy between the LKB and MPQ experiments as well as to find answers to many other questions related to the fundamental constants.

  • 14 November 2018

    No seminar because of CERN25 event of the Academy

  • 21 November 2018, Stefan Teufel (Tubingen)

    Non-equilibrium almost-stationary states and linear response for gapped quantum systems slides

    I report on recent mathematical results concerning the validity of linear response theory at zero temperature for perturbations of gapped Hamiltonians describing interacting fermions on a lattice, e.g. quantum Hall systems. The challenge here is to prove Kubo's formula uniformly in the volume and also for perturbations (like a small constant electric field) that close the spectral gap. Our justification of linear response theory is based on a novel extension of the adiabatic theorem to situations where a time-dependent perturbation closes the gap. According to the standard version of the adiabatic theorem, when the perturbation is switched on adiabatically and as long as the gap does not close, the initial ground state evolves into the ground state of the perturbed operator. The new adiabatic theorem states that for perturbations that are either slowly varying potentials or small quasi-local operators, once the perturbation closes the gap, the adiabatic evolution follows non-equilibrium almost-stationary states (NEASS) that we construct explicitly.

  • 28 November 2018, Peter Posfay (Wigner-MTA)

    Estimating the variation of neutron star observables by dense nuclear matter properties slides

    Description of extreme dense nuclear matter is an active research field, however Lattice QCD calcualtions are challenging for the case of cold dense matter. One needs effective theories to describe this region of the QCD matter and the consistency of these models can be constrained by studying compact astrophysical objects.

    Parameters corresponding to effective models of cold nuclear matter (interactions, coupling, mass) affect the observable parameters (mass and radius) of neutron stars. Moreover, detailed studies of QCD phase diagram shows the importance of bosonic quantum fluctuations. In this work we use the Functional Renormalization Group (FRG) method to take into account bosonic quantum fluctuations at fininte chemical potential at zero temperature. We did our caclulations in a system consisting of one fermionic and one bosonic degree of freedom, where the fermions and bosons are coupled together by a Yukawa coupling and the bosons have self interaction terms. We studied the effect of different interaction terms in the Lagrangian on the properties of nuclear matter.

  • 5 December 2018

    No seminar because of Zimanyi School

  • 12 December 2018, Gabor Biro (Wigner-MTA)

    Monte Carlo event generators in heavy-ion physics: a review slides

    In the recent decades the rapid technological advancement resulted in larger than ever collision energies, huge, complex detector systems, sophisticated readout systems with immense amount of experimental data, and therefore in the Golden Age of high-energy physics. Along with the experiments also the underlying theories went through a huge development. Nowadays the theoretical calculations are becoming more and more challenging, therefore numerical calculations are getting key importance, with special emphasis not just on the precision but on performance as well.

    In this talk I give a review on the Monte Carlo event generators used by the high-energy physics community. Through a historical perspective I introduce today's most widely used frameworks and I highlight the important aspects that emerged during their development and lead to their present state. I give also an outlook to the future's event generators, focusing on our HIJING++ project.

  • 13 February 2019, Andras Laszlo (Wigner-MTA)

    General Relativity experiment with spin polarized particle beams slides

    In experimental proposals published in the last two decades, a so called frozen spin storage ring concept emerged, for setting upper experimental bounds to electric dipole moment (EDM) of charged elementary particles with spin. In a recent paper of ours (Class.Quant.Grav.35(2018)175003), a fully covariant general relativistic (GR) calculation was presented on the Earth's gravitational modification effect on the spin transport inside such a frozen spin storage ring. It turns out that in certain configurations, Earth's gravity is expected to produce a similar order of magnitude effect as the aimed EDM sensitivity, and thus it becomes kind of realistic to experimentally see this GR effect. If such an experiment could be conducted, it could provide a novel test of GR: with microscopic particles, at relativistic speeds, along non-geodesic (forced) trajectories, and the tensorial nature of GR would be at test, not merely the gravitational drag. In more technical terms: the GR correction to the so called Thomas precession could be tested in lab. For details on the experimental idea, we refer to: arXiv:1901.06217 (Proceedings of Spin2018 Conference).

  • 20 February 2019, Ferenc Pittler (Bonn)

    A novel mechanism for dynamical generation of elementary fermion masses slides

    The Standard Model (SM) is very successful in describing a plethora of low energy phenomena, however it is unable to explain the electro-weak scale naturalness and the fermion mass hierarchy problem. In this talk we numerically verify an intrinsically non-perturbative mechanism for elementary fermion mass generation advocated in 1402.0389 using lattice QCD techniques. This mechanism takes place in non-Abelian gauge models if fermionic chiral symmetries are explicitly broken at the UV cutoff scale and an exact invariance acting on both fermions and scalars forbids power divergent fermion mass corrections. We argue that a complete, composite Higgs-like beyond SM (BSM) scenario can be built using this mass generation mechanism. We also discuss differences-similarities with respect to the current BSM models studied with lattice simulations.

  • 27 February 2019, Mate Csanad (Eotvos)

    The RHIC(+SPS+FAIR+NICA+JPARC) Beam Energy Scan Program slides

    The RHIC beam energy scan program, complemented by similar programmes at other accelerators, allows for the investigation of the phase diagram of QCD matter by varying the beam energy in the region where the change from crossover to first order phase transition is suggested to occur. The nature of the quark-hadron transition can be studied through analyzing the space-time structure of the hadron emission source. Many measurements were performed in the recent years, from spectra and yields through fluctuations and anisotropies to intermittency and quantumstatistical correlations. These as of now show a controversial picture, and in this talk, we will go through the plethora of results, with special focus on Bose-Einstein correlations.

  • 6 March 2019, Koushik Mandal (Eotvos)

    Fully Hadronic SUSY Search in CMS slides

    Supersymmetry (SUSY) is one of the best motivated and most compelling theories going beyond Standard Model (SM) physics. In the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC), SUSY searches have been extensively carried out exploring the possibility of the existence of the supersymmetric partners of SM particles in a wide mass range studying diverse experimental signatures. Given the naturalness theory, the scalar top quarks and the gluino are of particular interest. Depending on the final state of the scalar top and gluino decays, search channel could be leptonic, hadronic or mixed. Because of the higher expected rate at the LHC, we studied the fully hadronic final state containing missing transverse momenta and multiple jets. A comprehensive study of stop and gluino searches will be presented, underlining the method to tag top quark decays and to estimate from the LHC data the SM background rate.

  • 13 March 2019, Ruchi Chudasama (Eotvos)

    Physics of ultra-peripheral collisions with CMS experiment slides

    Moving highly-charged ions carry strong electromagnetic fields that act as a beam of photons. In collisions at large impact parameters, hadronic interactions are not possible, and the ions interact through photon-photon and photon-ion collisions known as ultra-peripheral collisions (UPCs). Photon-photon interactions provide a wide range of opportunities from the test of Quantum Electro-Dynamic (QED) to search for physics beyond Standard Model (SM). We provide the evidence for light by light scattering and search for axion-like particles using high photon fluxes from PbPb collisions. On the other hand, photon-ion processes can probe the gluon distribution in proton and heavy-ions down to Bjorken -x values 10^{-6}, far smaller than can be otherwise studied. In this low-x regime, non-linear QCD effects (gluon recombination) may become important, possibly leading to the saturation of the parton distribution functions. We probe the parton distribution inside proton by studying the exclusive upsilon photoproduction in pPb collisions.

  • 20 March 2019, Antal Jakovac (Eotvos)

    Bound states in quantum field theory: an FRG study

    In the talk we review the traditional approaches to define bound states in quantum theories. In the example of QED with two oppositely charged fermionic fields, we demonstrate the construction of an effective model that contains bound states, and which reproduces the fermionic observables of the original model. Using numerical analysis in the nonrelativistic limit, we argue that considerable simplifications can be made, still maintaining a reasonable accuracy in the computation of the ground state energy.

  • 27 March 2019, Gergely Marko (Eotvos)

    Magnetic field dependence of the NJL coupling from lattice QCD slides

    Chiral effective models of strong interactions struggle to capture the inverse magnetic catalysis observed in continuum extrapolated lattice results. One recent trend is to incorporate absent degrees of freedom by making effective model parameters depend on B. We try to improve on this approach by deducing the magnetic field dependence of the Nf=2 (P)NJL coupling directly from lattice observables. We carried out full lattice QCD simulations for the baryon octet masses as a function of the magnetic field using staggered fermions. A continuum extrapolated result is obtained in the eB < 0.6 GeV^2 region. Using a simple non-relativistic quark model we infer constituent quark masses from the baryons which in turn serve as inputs to obtain the B-dependent coupling. We then solve the (P)NJL model to assess the effect of the B-dependent coupling on the pseudo-critical temperature of the chiral phase transition.

  • 12 April 2019, Slava Rychkov (IHES, Ecole Normale Superieure Paris)

    Walking, weakly first-order phase transitions, and complex CFTs

    Most people have heard that the 2d Potts model with Q=5 states has a first order phase transition, but not everyone knows that the correlation length at this phase transition is 2500 lattice spacings. We will review "walking RG" behavior in gauge theories and connect it to Type II weak first-order phase transitions in statistical physics. Despite appearing in very different systems (QCD below the conformal window, the Potts model, deconfined criticality) these two phenomena both imply approximate scale invariance in a range of energies and have the same RG interpretation: a flow passing between pairs of fixed point at complex coupling, dubbed "complex CFTs". Observables of the real walking theory are approximately computable by perturbing the complex CFTs. The general mechanism will be illustrated by a specific and computable example: the two-dimensional Q-state Potts model with Q > 4. Based on 1807.11512 and 1808.04380.

  • 24 April 2019, Laurent Lellouch (CNRS, Aix-Marseille U)

    Hadronic vacuum polarization contribution to the muon magnetic moment from lattice QCD slides

    In the early 2000s, the anomalous magnetic moment of the muon, a_mu=(g_mu-2)/2, was measured with a remarkable precision of 0.54ppm. Since those results were published, a discrepancy of more than 3 standard deviations has persisted between the standard model (SM) prediction and experiment. At present theoretical and experimental uncertainties are close in size. However, a new experiment underway at Fermilab is aiming to reduce the experimental uncertainty on a_mu by 4. To leverage this future measurement and possibly claim the presence of new fundamental physics, it is imperative to reduce and fully control the uncertainties in the SM prediction. After an introduction to the role that anomalous magnetic moments play in testing the SM and a discussion of the current experimental and theoretical status of a_mu, I will present a lattice QCD calculation of the contribution to this quantity that most limits the precision of its SM prediction.

  • 8 May 2019, Mordehai Milgrom (Weizmann Institute, Israel)

    Scale invariance at low accelerations as an alternative to dark matter slides

    Galactic systems, and the Universe at large, exhibit much larger accelerations than are predicted by Newtonian dynamics and general relativity, if only the matter we actually observe is responsible for gravity. The mainstream comes to the rescue of these revered paradigms by invoking large quantities of `dark matter' -- which purportedly supplies the needed extra accelerations -- and also of `dark energy', to account for the unexplained accelerated expansion of the Universe. The MOND paradigm offers a different solution: a breakdown of standard dynamics (gravity and/or inertia) in the limit of low accelerations -- below some acceleration a_0. In this limit, dynamics become space-time scale invariant, and is controlled by a gravitational constant A_0 ~ G a_0, which replaces Newton's G. With the new dynamics, the various detailed manifestations of the anomalies in galaxies are predicted with no need for dark matter. An intriguing aspect of MOND is that the MOND constant turns out to carry cosmological connotations: a_0 ~ c^2/R_U, R_U being `the radius of the Universe'. There are MOND theories in which this `coincidence' is natural. I draw on enlightening historical and conceptual analogies to limelight aspects of MOND.

  • 15 May 2019, Robert Harlander (Aachen)

    Gradient flow at higher orders in perturbation theory slides

    The implementation of a systematic approach to the perturbative calculation of Green's functions in the gradient-flow formalism is described. Results for the conversion of the gradient-flow coupling to the MSbar scheme, and an analogous relation for the quark mass are presented through next-to-next-to-leading order (NNLO) QCD. As a second application, the gradient-flow definition of the energy-momentum tensor through NNLO QCD will be considered. The relevance of the higher-order effects will be highlighted by studying their impact on the theoretical uncertainty estimate.

  • 29 May 2019, Sho Iwamoto (Padova)

    SUSY status at the LHC, focusing on the muon g-2 anomaly and dark matter slides

    The Run-2 LHC provided sufficient data to search for "non-colored" TeV-scale new particles. Before the Run 2, I expected that we would discover such "non-colored" particles that are predicted by TeV-scale SUSY, because they may solve an anomaly of the muon g-2 and also can explain the origin of the dark matter.

    Unfortunately, it seems that my expectations do not fulfill. One piece of good news is that we have a new measurement of the muon g-2, which will publish their results later this year. If it confirms the anomaly, then it may tell us that the non-colored SUSY particles are hidden somewhere in the parameter space and evading from our search strategy. In this talk, we review the LHC status of TeV-scale SUSY, focusing on the muon g-2 anomaly and the dark matter, and discuss possibilities of this hide-and-seek.

    In addition, I will be talking briefly on two other recent works of mine: leptogenesis on "neutrino option" models, and dark matter models with new confining gauge group, as an introduction of myself to the ELTE people.

  • 12 June 2019, Laszlo Csernai (University of Bergen)

    Laser driven ignition for inertial confinement fusion slides

  • 4 September 2019, Marton Lajer (Wigner-ELTE)

    Truncated Spectrum Approach to the sinh-Gordon model and its generalizations

    We consider a class of models obtained by perturbing the non-compact Gaussian CFT with two vertex operators. These include the integrable sinh-Gordon and Bullough-Dodd models as special cases. The above theories are special as they can be considered equivalently as perturbations of Liouville CFTs, and the consistency between these viewpoints leads to interesting properties. We apply the Truncated Spectrum Approach (TSA) to these models. Despite apparent problems regarding the perturbative RG improvement, we argue that TSA is applicable as long as both related Liouville models are below the self-dual point. We check that the small-volume asymptotics of the spectrum is described by a quantization condition involving the Liouville reflection amplitude even in the non-integrable case. It has long been known that the reflection amplitude also appears in a set of functional equations describing the VEVs of vertex operators. The analytic ?minimal? solution thereof is numerically confirmed to provide the exact expectation values in both integrable subsets. We find that the similar ?minimal? solution with respect to the general, non-integrable models still provides a good approximation over a wide range of parameter space (even though it is not exact). In the case of VEVs, TSA always breaks down just before reaching the first zeroes of the minimal solution, which coincide with the Seiberg bounds of the related Liouville theories.

  • 18 September 2019, Miguel Tierz (Universidade de Lisboa)

    Matrix models and Chern-Simons theory slides

    We first give an introduction to the basics of random matrix theory, with an emphasis on its relevance in gauge theory. We then focus on the description, in terms of matrix models, of Chern-Simons theories, including the case of theories with supersymmetric matter.

  • 2 October 2019, Gabor Etesi (BME)

    The four dimensional Yang--Mills partition function in the vicinity of the vacuum

    In this lecture we outline the computation of the partition function of four dimensional Euclidean, non-supersymmetric SU(2) Yang--Mills theory in the perturbative and weak coupling regime i.e. in a small open ball about the flat connection (what we call the "vicinity of the vacuum") and when the gauge coupling constant acquires a small but finite value.

    The computation is based on various known inequalities, valid only in four dimensions, providing two-sided estimates for the exponentiated Yang--Mills action in terms of the L^2-norm of the derivative of the gauge potential only; these estimates then give rise to Gaussian-like infinite dimensional integrals involving the Laplacian hence can be formally computed via zeta-function and heat kernel techniques. It then turns out that these integrals give a sharp value for the partition function in the aforementioned perturbative and weak coupling regime of the theory.

    A physical interpretation of the resulting closed formula in the realm of asymptotic freedom is also exhibited.

    More details: 1907.05669 [hep-th]

  • 9 October 2019, Gergely Fejos (Eotvos)

    Axial anomaly and hadronic properties in a nuclear medium slides

    I will show recent results on meson and nucleon dynamics at finite baryon density and temperature, by coupling the nucleon field and the omega meson to the three flavor linear sigma model. Using the functional renormalization group (FRG) method, I will show how to calculate hadronic properties at the nuclear liquid-gas transition, and argue that mesonic fluctuations increase the strength of the coefficient of the U_A(1) breaking determinant operator. Density dependence of the meson masses and partial restoration of chiral symmetry will also be discussed.

  • 16 October 2019, Janos Balog (Wigner)

    Non-linear sigma model and the Maxwell-Kirchhoff electrostatic problem slides

    Three different physical systems: the O(N) nonlinear sigma model and the Lieb-Liniger model in 1 dimension, and the parallel disks capacitor, are all described by (nearly) the same TBA-type integral equation. Sigma model perturbation theory, which is completely solved, provides solutions for the two other systems as well. The disk capacitor problem has historical interest, mainly because in the past many famous physicists took up the challenge of solving it.

  • 30 October 2019, Ralf Ulrich (Karlsruhe)

    Importance of dedicated LHC measurements for cosmic ray physics slides

    When ultra-high energy particles from astrophysical objects arrive at earth they cannot be detected directly. They interact with the atmosphere and produce huge extensive air shower cascades. Such cascades can be experimentally observed easily and are our only handle to study the universe at the highest energies. By their nature, air showers fundamentally connect particle physics and astrophysics together. The microscopic processes in the air showers must be understood precisely to make best use of the recorded data. The LHC plays a crucial role in studying such processes in detail.

  • 6 November 2019, Timo Karkkainen (Eotvos)

    Unexpected alliance: 331-model with Froggatt-Nielsen and linear seesaw mechanisms slides

    We propose a model to naturally explain the fermion mass hierarchies, neutrino masses and oscillations and the number of generations. Minimal field content of SU(3)$_C \otimes$ SU(3)$_L \otimes$ U(1)$_X$ gauge symmetry group along with heavy sterile right-handed Majorana neutrinos is sufficient. The flavon scalar, instrumental in Froggatt-Nielsen mechanism, is already included in minimal 331-model. The neutrino masses are generated to three mass scales: sub-eV-, keV- and TeV-scales. The seesaw scale, 331-symmetry breaking scale and Froggatt-Nielsen scale are nearly same. We present an example scenario which produces the Standard Model and neutrino parameters within the experimental limits.

  • 13 November 2019, Josu Hernandez (Eotvos)

    Neutrino masses and mixings, and a possible new Weinberg operator slides

    Despite the remarkable agreement between a wide range of SM predictions and their experimental measurements, the SM has to be extended in order to explain the overwhelming experimental evidence from the neutrino oscillation phenomena supporting the existence of neutrino masses and mixings, which are absent in the SM. A simple and natural extension to account for neutrino masses is to introduce right-handed neutrinos in the particle content of the SM. Since these extra right-handed neutrinos are singlets under the SM gauge group, a Majorana mass term for these fermions is therefore allowed in the Lagrangian.

    One possibility is that this Majorana scale is above the EW scale but in the 100 GeV-TeV range. Then, the masses of the left-handed neutrinos arise in a simple way after ESB through the Weinberg operator in a low scale SM-Seesaw. In this situation, the presence of the new degrees of freedom will induce deviations from unitarity in the leptonic mixing matrix that appears in the charged current interactions. Thus, processes mediated by the weak currents would be modified, and therefore precision measurements of electroweak and flavor observables become a powerful tool to probe for the existence of heavy Majorana neutrinos.

    Since heavy particles with large Yukawa couplings can induce sizeable radiative corrections, the importance of higher order corrections from right-handed neutrino loops when deriving bounds on their mixing with the light active states has been studied (arXiv:1508.03051). Then, a global fit to the most complete and updated stringent set of electroweak and flavour observables to constrain the mixing of the extra heavy right-handed neutrinos in a model independent way has been performed (arXiv:1605.08774). The bounds derived in this work apply to any extension of the SM with heavy right-handed neutrinos. In particular, they constrain regions of the parameter space of a model with two different Higgs doublets and a fourth vector-like family charged under a U(1)' gauge group (arXiv:1903.01474). In this model, neutrino masses are generated through a new Weinberg operator that mixes the two Higgs doublets and the heavy vector-like neutrinos in a Type Ib Seesaw.

  • 20 November 2019, Carlos Pena (Universidad Autonoma de Madrid)

    Old problems and new(?) physics: non-leptonic kaon decay and the DeltaI=1/2 rule slides

    I will review the status of our understanding of non-leptonic kaon decay, a classic problem that was born, grew, and has matured alongside the Standard Model and the quest for new fundamental physics. Beyond state-of-the-art quantitative results, I will focus on a strategy to understand the mechanism responsible for the DeltaI=1/2 enhancement, that brings together a large toolset of field-theoretical methods. The most recent results, based on large N techniques, also allow for additional insight into light meson dynamics.

  • 27 November 2019, Michael Trott (University of Copenhagen)

    Developments of the Standard Model Effective Field Theory slides

    After the discovery of the Higgs like boson at LHC, particle physics entered into an era where the current model can be extrapolated to energies parametrically separated from the electroweak scale, without any internal theoretical inconsistency. As a result, the Standard Model treated as a well defined Effective Field theory (SMEFT) emerged. This theory is of interest for phenomenological studies of LHC and lower energy data, and also as a formal field theory. I will discuss some of the developments of this form that have appeared in recent years, and sketch out the future physics program of the SMEFT.

  • 4 December 2019

    No seminar, Zimanyi Winter School and Workshop

  • 11 December 2019, Robert Vertesi (Wigner)

    Heavy-flavour measurements with the ALICE experiment at the LHC slides

    The Large Hadron Collider (LHC) at CERN investigates the fundamental nature of the strong interaction in collisions of protons or heavy ions that are travelling at almost the speed of light. In these high-energy collisions, heavy (charm and bottom) quarks are created in the early stages of the reaction. Since they are produced in initial hard processes and their numbers are largely unchanged in the later stages of the reaction, they serve as ideal probes to test the validity of quantum color dynamics as well as the properties of a strongly interacting hot and dense medium in a heavy ion collision. In small collision systems we can use them for detailed tests of pQCD models as well as flavor-dependent fragmetation. Launched in 2015, the LHC's Run-II phase, with the improved ALICE detector system, enabled the most precise heavy quark measurements ever. This talk presents some of the most intriguing recent heavy-flavor results from ALICE, along with phenomenological considerations that motivate new studies.

  • 18 December 2019, Zoltan Peli (MTA-DE)

    Particle physics model of curvaton inflation in a stable universe

    TBA

  • 12 February 2020, Tamas G Kovacs (Eotvos) slides

    Instanton interactions in high temperature QCD

    In high temperature QCD instantons are expected to form a dilute gas amenable to analytic treatment. However, the analytically computed temperature-dependence of the topological susceptibility differs significantly from the susceptibility obtained in recent lattice calculations that are relevant to axion physics. A key assumption of the dilute instanton approximation is that instantons (and antiinstantons) form a non-interacting ideal gas. In the talk I will show that spectra of lattice Dirac operators with exact chiral symmetry provide a tool to study instanton interactions above the temperature of the chiral and deconfining transition. A detailed analysis of the lowest part of the Dirac spectrum also yields new insight into the nature of the chiral and deconfining transition and their connection to quark localization.

  • 19 February 2020, Matteo Giordano (Eotvos) slides

    Localisation and Goldstone bosons at finite temperature

    I discuss spontaneous breaking of chiral symmetry in gauge theories with fermions at finite temperature when localised modes are present in the spectrum of the Dirac operator. In particular, I show how localised Dirac modes affect the Goldstone poles that are expected to show up in certain correlation functions when a continuous symmetry is spontaneously broken.

  • 26 February 2020

    No seminar, talk by Istvan Csabai at the Academy

  • 4 March 2020, Sinya Aoki (Yukawa Institute, Kyoto) slides

    Holography from field theories: a realization of AdS/CFT correspondence and beyond

    We argue that the Anti-de-Sitter (AdS) geometry in d+1 dimensions naturally emerges from an arbitrary conformal field theory in d dimensions using the free flow equation. We first show that an induced metric defined from the flowed field generally corresponds to the quantum information metric, called the Bures or Helstrom metric, if the flowed field is normalized appropriately. We next verify that the induced metric computed explicitly with the free flow equation always becomes the AdS metric when the theory is conformal. We also show that the conformal symmetry in d dimensions converts to the AdS isometry in d+1 dimensions after d dimensional quantum averaging. This guarantees the emergence of AdS geometry without explicit calculation.

    We next apply this method to non-relativistic systems with anisotropic scaling symmetries, such as Lifshitz field theories and Schrodinger invariant theories. In consequence we obtain a new hybrid geometry of Lifshitz and Schrodinger spacetimes as a general holographic geometry. We also show that the bulk hybrid geometry is realized by an Einstein-Maxwell-Higgs system plus a gauge fixing term for diffeomorphism, which may be interpreted as a holographic dual of a general non-relativistic system at the boundary.

  • 11 March 2020, Mate Lencses (BME) slides

    Chiral Entanglement in Quantum Field Theories in 1+1 Dimensions

    The fixed points of the renormalization group (RG) in quantum field theory can be characterized by conformal field theories (CFTs). In 1+1 dimensions the spectrum of the CFT consists of left and right moving chiral excitations. One can consider the chiral entanglement entropy, the entanglement entropy in ground states between the left and right chiral degrees of freedom. In the fixed point CFT the chiral entanglement entropy is zero and it is finite away from criticality. Moreover, it scales linearly with the system size with a mass dependent slope in the large system limit, and contains a universal constant term, which characterizes the RG flow. Based on the variational Ansatz proposed by J. Cardy, we study the chiral entanglement entropy of ground states along massive RG flows. The analytical results are compared to numerical calculations using the truncated conformal space approach for RG flows around the Ising and tricritical Ising fixed points.

  • 18 March 2020, Tamas Kovacs (Eotvos)

    Cancelled because of COVID-19

  • 15 April 2020, Sven Moch (Hamburg University)

    Cancelled because of COVID-19

  • 22 April 2020, Kornel Kapas (Eotvos)

    Cancelled because of COVID-19

  • 13 May 2020, John Gracey (Liverpool)

    Cancelled because of COVID-19

  • 20 May 2020, Masanori Hanada (Southampton)

    Cancelled because of COVID-19

  • 19 June 2020, Attila Pasztor (Eotvos), online zoom

    Constraining the QCD phase diagram with analytic continuation

    I review the basic methods of analytical continuation from numerical data, and discuss some recent results on the QCD phase diagram obtained with these methods. I also discuss the status of some ongoing projects.

  • 23 September 2020, Tamas Kovacs (Eotvos) slides

    Prediction of chaotic time series -- a machine learning approach

    Recently, it turned out that recurrent neural network (RNN) is an extremely successful concept to forecast nonlinear dynamical systems. However, it is computationally expensive to train all the parameters in a nonlinear optimization problem. In this talk I am going to review a special case of RNNs, the reservoir computing (RC), that fits also perfectly to the task of forecasting. In RC only the output layer must be trained with many few parameters and a cheap linear least square operation. The method will be introduced step by step through practical examples.

  • 30 September 2020, Zoltan Peli (Debrecen) slides

    Derivative expansion for computing critical exponents of O(N) symmetric models at NNLO accuracy

    We apply the derivative expansion of the effective action in the exact renormalization group (ERG) equation up to fourth order (\partial^4-order, NNLO) on the Z_2 and O(N) symmetric scalar models in d=3 Euclidean dimensions. We compute the critical exponents nu, eta and omega using polynomial expansion in the field. We obtain our predictions for the exponents employing two regulators widely used in ERG computations. We find that both regulators produce results in agreement with predictions obtained by the available Monte-Carlo and conformal bootstrap methods, but requiring significantly less computational time than those do.

  • 7 October 2020, Gergely Fejos (Eotvos) slides

    Order of the color superconducting phase transition

    I will present recent results on the finite temperature phase transition of color superconductivity, predicted to exist in dense quark matter. By reviewing renormalization group analyses of ordinary superconductivity, I will generalize its Ginzburg-Landau functional to QCD and calculate the flow of the free energy in three spatial dimensions via the functional renormalization group technique. The findings show that unlike ordinary superconductivity, the color superconducting phase transition can only be of first order.

  • 14 October 2020, Peter Bantay (Eotvos) slides

    Gauge Lattice Theory

    We give an overview of some recent advances in the field, with special emphasis on computational issues.

  • 21 October 2020, Sven Moch (Hamburg)

    QCD evolution at 1% precision

    We review the status and precision of evolution equations in perturbative QCD. We give an overview on the current theoretical status and the calculational techniques used in perturbation theory. We discuss the application of QCD evolution equations in the determination of parton distribution functions in the proton, the strong coupling constant alpha_s and the quark masses m_c, m_b and m_t in global fits. We give an overview of current results and compare to available information from other approaches like lattice QCD.

  • 28 October 2020, Balazs Pozsgay (Eotvos) slides

    Non-equilibrium dynamics of integrable models: Brief review and current research projects

    This is an introductory talk for the ,,Momentum'' Integrable Quantum Dynamics research group, which was started in September 2020 at the Department of Theoretical Physics, Eotvos Lorand University. We review the history of one dimensional integrable quantum systems, with special emphasis on non-equilibrium problems and the developments of the last decade. We discuss the concept of the Generalized Gibbs Ensemble, and also the recent theory of Generalized Hydrodynamics (GHD), describing the transport properties of these models. Finally we discuss a few open questions, and ongoing and planned future projects of the group.

  • 4 November 2020, Josu Hernandez-Garcia (Eotvos) slides

    GeV-scale neutrinos: interactions with mesons and DUNE sensitivity

    The simplest extension of the SM to account for the observed neutrino masses and mixings is the addition of at least two singlet fermions (or right-handed neutrinos). If their masses lie at or below the GeV scale, such new fermions would be produced in meson decays. Similarly, provided they are sufficiently heavy, their decay channels may involve mesons in the final state. Although the couplings between mesons and heavy neutrinos have been computed previously, significant discrepancies can be found in the literature. The aim of this talk is to clarify such discrepancies and provide consistent expressions for all relevant effective operators involving mesons with masses up to 2 GeV. As an application, we numerically compute the expected sensitivity of the DUNE near detector to these heavy neutral leptons.

  • 11 November 2020, Gyula Bene (Eotvos) slides video

    Covariance with respect to canonical transformations - a unification of gravity and electromagnetism?

    Coordinate transformation of general relativity and gauge transformation of classical electrodynamics are considered as special canonical transformations in eight dimensional relativistic phase space of charged massive particles. Question is raised if it is possible to formulate the laws of physics that are covariant with respect to any canonical transformations. A partial answer is presented: the geometry of phase space is characterized by suitable connections which are explicitly expressed in terms of electromagnetic potentials and the metric tensor. Motion of a charged, massive particle is geodetic motion in this geometry. A possible way to derive field equations in phase space is also discussed.

  • 18 November 2020, Arthur Hutsalyuk (Eotvos) slides

    The LeClair-Mussardo series and Bethe ansatz

    Correlation functions in numerous 1D quantum integrable systems can be calculated using a special type of ansatz called the Bethe ansatz. Diagonal form factors of physical operators can be computed explicitly in the case of systems with a small number of (quasi)particles. Then the correlation functions of the operators can be expanded in the series of symmetric form factors, which are the analytical continuation of the physical form factors. Such expansion, called LeClair-Mussardo series, provides us with the simple method for computations of multi-point correlation functions in a case the series has reasonably good convergence properties. The case of 1D Fermi gas will be considered. The talk is based on the work arXiv:2009.13203, The LeClair-Mussardo series and nested Bethe Ansatz, Arthur Hutsalyuk, Balazs Pozsgay, Levente Pristyak.

  • 25 November 2020, Marton Lajer (Wigner) slides video

    Truncated spectrum methods and the self-duality of the sinh-Gordon model

    One of the most striking but mysterious properties of the sinh-Gordon model (ShG) is the b -> 1/b self-duality of its S-matrix, of which there is no trace in its Lagrangian formulation. Here b is the coupling appearing in the model's eponymous hyperbolic cosine present in its Lagrangian, cosh( b phi ). We have developed truncated spectrum methods (TSMs) for studying the sinh-Gordon model at a finite volume as we vary the coupling constant. We obtain the expected results for $b >> 1$ and intermediate values of b, but as the self-dual point b=1 is approached, the basic application of the TSM to the ShG breaks down. We find that the TSM gives results with a strong cutoff E_c dependence, which disappears according only to a very slow power law in E_c. Standard renormalization group strategies -- whether they be numerical or analytic -- also fail to improve upon matters here. In our recent paper we explore different strategies to circumvent the limitations of TSM in the vicinity of b=1. In this talk I will focus in particular on the use of exact form factors to treat the ShG at one value of b as a perturbation of a ShG at a different coupling. I will argue that the strong coupling phase b > 1 of the Lagrangian formulation of model may be different from what is naively inferred from its S-matrix. An argument will be given that the theory is actually massless for b > 1. The talk is based on R. Konik, M. Lajer, G. Mussardo, arXiv:2007.00154 (recently accepted for publication by JHEP)

  • 2 December 2020, Tamas Gombor (Eotvos) slides video

    Integrable boundary states in AdS/CFT

    This is an introductory talk for the application of integrability techniques in the AdS/CFT correspondence. We review the Maldacena's argument for the duality between the N=4 super Yang-Mills theory and the type IIB superstring theory on AdS_5 x S^5. I will briefly show how the integrability works for the calculation of anomalous dimensions of primary fields. After that I will introduce other interesting physical quantities (e.g. one-point function in defect versions of N=4 SYM) whose calculation can be traced back to determine overlaps between multi-particle wave function and some special states called boundary states. We will see that these boundary states fit nicely into the integrability framework. Finally, I will summarize the resent status of calculation of one-point functions and the contribution of me and my collaborators to this topic.

  • 9 December 2020, Daniel Nogradi (Eotvos) slides

    Revisiting the semi-classical approximation at high temperature

    It is possible to obtain unambiguous and reliable predictions from QCD using perturbation theory and semi-classical methods at high temperature. One would think the size distribution of instantons and the topological susceptibility are standard examples probably already calculated a long time ago. We will show that the over-all normalization of the semi-classical result was so far used incorrectly in the literature in MS-bar and the numerical uncertainty of a temperature dependent factor is two orders of magnitude larger than originally claimed. Both issues are corrected, making comparison of non-perturbative lattice results and the semi-classical predictions possible at high temperature. Based on 2001.03383.

  • 9 February 2021, Robert Vertesi (Wigner) slides

    Scaling properties of jets in high-energy pp collisions

    Measurements of jet profiles in high-energy collisions are sensitive probes of QCD parton splitting and showering. Precise understanding of the jet structures are essential for setting the baseline not only for nuclear modification of jets in heavy-ion collisions, but also for possible cold QCD effects that may modify jets in high-multiplicity proton-proton collisions. In this talk we demonstrate that the radial jet profiles in proton-proton collisions exhibit scaling properties with charged-hadron event multiplicity over a broad transverse-momentum range. Based on this we propose that the scaling behavior stems from fundamental statistical properties of jet fragmentation.

    We also study the multiplicity distributions of events with hard jets and show that the charged-hadron multiplicity distributions scale with jet momentum. This suggests that the Koba--Nielsen--Olesen (KNO) scaling holds within a jet. The in-jet scaling is fulfilled without multiple-parton interactions (MPI), but breaks down in case MPI is present without color reconnection. Our findings imply that KNO scaling is violated by parton shower or multiple-parton interactions in higher-energy collisions.

  • 16 February 2021, Gabor Biro (Wigner) slides

    The Tsallis-Thermometer as a QGP Indicator For Large And Small Collisional Systems

    The transverse momentum distribution of identified hadrons are analyzed within the thermodynamically consistent formulation of non-extensive statistics. A wide range of center-of-mass energies and average event multiplicities are studied for various hadron species. We demonstrate that the average event multiplicity is a key variable in the study of high-energy collisions. For this purpose the non-extensive statistical approach is more than appropriate.

    Recent experimental results present collectivity also in small systems with high-multiplicity. Today these phenomena are not completely understood: it is an important question whether the presence of the QGP is necessary for the observed collectivity or not. Moreover, the connection between the experimental observables and theories is not trivial. In our phenomenological study we introduce the 'Tsallis-thermometer' as an indicator of quark-gluon plasma, that aims to describe the smooth transition from small to large collisional systems.

    Based on

    [1] G. Biro, G.G. Barnafoldi, T.S. Biro, J. Phys. G, 47.10 (2020), 105002.

    [2] G. Biro, G.G. Barnafoldi, K. Urmossy, T.S. Biro, A. Takacs, Entropy, 19(3), (2017), 88

    [3] G. Biro, G.G. Barnafoldi, T.S. Biro, K. Shen, EPJ Web Conf., 171, (2018), 14008

    [4] G. Biro, G.G. Barnafoldi, G. Papp, T.S. Biro, Universe 5 (2019) no.6, 134

  • 23 February 2021, Zoltan Bajnok (Wigner) slides

    From perturbative to non-perturbative in the O(4) sigma model

    Is it possible to derive non-perturbative contributions in a quantum field theory knowing only the perturbative coefficients? We answer this question affirmatively based on the careful analysis of the integrable two dimensional O(4) sigma model. We investigate its ground state energy in a magnetic field, for which integrability provides an exact linear integral equation. By cleverly expanding this equation we could calculate a large number of very percise, factorially growing perturbative coefficients. By investigating their asymptotical behaviour on the Borel plane we managed to reveal a nice resurgence structure leading to the first few exponentially supressed non-perturbative terms of the ambiguity free trans-series. We checked our results against the direct numerical solution of the exact integral equation and find complete agreement. Based on 2011.12254 and 2011.09897.

  • 2 March 2021, Daniel Kincses (Eotvos) slides

    Investigating the pion source-function in heavy-ion collisions

    By measuring the momentum correlations of pions created in heavy-ion collisions one can gain information about the space-time geometry of the particle emitting source. Recent experimental results from multiple different collaborations demonstrated that to properly describe the shape of the measured correlation functions, one needs to go beyond the Gaussian approximation. Some studies suggest that the Levy distribution could provide a good description of the source. While there are already many experimental results, there is very little input from the phenomenology side in explanation of the observed non-Gaussian source shapes. In my talk I will cover the basics of heavy-ion collisions and the field of femtoscopy, and discuss both experimental and phenomenological studies of the pion emitting source.

  • 9 March 2021, Simon Knapen (CERN) slides

    Soft signals at the high luminosity LHC

    The LHC is both a Higgs and B-factory, and for both particles it will deliver the largest data set for many decades to come. I will discuss a few examples of ways we can leverage this to search for beyond the Standard Model physics during the high luminosity phase of the LHC.

  • 16 March 2021, Gergely Barnafoldi (Wigner) slides

    Estimating nuclear matter parameters from compact star observables: a traditional methods vs. brute force

    In this study we estimated the parameters of the extended sigma-omega model for neutron star matter by two methods. First, in a traditional way, we assumed that pulsars PSR J0740+6620, PSR J0348+0432, and PSR J1614?2230 are maximal mass compact star, which led us to apply the 'core approximation' and use the observed linear relations between the microscopic and macroscopic parameters of neutron stars suggested by this model. Here we estimated the values of the nucleon Landau mass and nuclear compressibility [1,2]. In a second case, we used the 'brute force method': applying the Bayesian analysis on many, state-of-the-art multi-messenger astronomy observation data on mass, radius, and tidal deformabilities as well. We have considered the nuclear parameters above including the (a)symmetry energy at saturation density [3,4]. As a result, we were able to compare the two independent methods and the most probable values of the nuclear matter parameters of neutron star core were estimated.

    Based on:

    [1] arXiv 2004.08230

    [2] Eur.Phys.J.ST 229 (2020) 22-23, 3605-3614

    [3] Eur.Phys.J.ST 229 (2020) 22-23, 3615-3628

    [4] Phys.Part.Nucl. 51 (2020) 4, 725-729

  • 23 March 2021, Yoshikazu Nagai (Eotvos)

    delayed

  • 30 March 2021, Biplab Dey (Eotvos) slides

    Latest highlights from LHCb

    As the first dedicated B-factory at a hadron collider, LHCb looks for signals of New Physics through precision measurements in the flavor sector. After a brief introduction, I will discuss some of the latest results on exotic hadron spectroscopy and anomalous measurements in the b->s electroweak penguin sector.

  • 6 April 2021

    spring break

  • 13 April 2021, Mihaly Pocsai (Wigner) slides

    Hydrodynamical Evolution of a Self-gravitating Dark-fluid Universe

    We present a dark fluid model which contains the general linear equation of state including the gravitation term. The obtained spherical symmetric Euler equation and the continuity equation was investigated with the Sedov-type time-dependent selfsimilar Ansatz which is capable to describe physically relevant diffusive and dispersive solutions. The role of the parameter in the equation of state is investigated. As results the space and time dependent fluid density and radial velocity fields are presented and analyzed. Additionally, the role of the initial velocity on the kinetic and total energy of the fluid is discussed.

  • 27 April 2021, Gergely Fejos (Eotvos) slides

    Non-perturbative renormalization of field dependent couplings

    I will discuss the importance of field dependent couplings in field theories, in particular those relevant in low energy strong interactions. Non-perturbative (functional) renormalization group flows will be shown for Yukawa type interactions and that of the axial anomaly in the three-flavor meson model. Particular emphasis will be put on choosing appropriate background fields for practical computations and numerical results will be presented for physical parametrizations.

  • 11 May 2021, Zoltan Fodor (Penn State) slides

    (g-2)_mu from lattice QCD and experiments: 4.2 sigma, indeed?

    Twenty years ago, in an experiment at Brookhaven National Laboratory, physicists detected what seemed to be a discrepancy between measurements of the muon's magnetic moment and theoretical calculations of what that measurement should be, raising the tantalizing possibility of physical particles or forces as yet undiscovered. The Fermilab team has just announced that their precise measurement supports this possibility. The reported significance for new physics is 4.2 sigma just slightly below the discovery level of 5 sigma. However, an extensive new calculation of the muon's magnetic moment using lattice QCD by the BMW-collaboration reduces the gap between theory and experimental measurements. The lattice result appeared in Nature on the day of the Fermilab announcement. In this talk both the theoretical and experimental aspects are summarized with two possible narratives: a) almost discovery or b) Standard Model re-inforced. Some details of the lattice caluculation are also shown.

  • 18 May 2021, Sho Iwamoto (Eotvos) slides

    (g-2)_mu for SUSY (and models beyond the Standard Model)

    The latest Fermilab measurement established a 4-sigma anomaly on the muon g-2, compared to the Standard Model predition. We had a seminar talk by Zoltan, which suggests that the anomaly is due to the Standard Model prediction of the "HVP" conbtribution. I will talk about the remaining possibility of the interpretation, i.e., the new physics interpretations of the anomaly. First I will briefly review new physics scenarios for the anomaly; we will then focus on "SUSY" explanation of the anomaly and discuss the connection of the muon g-2, the dark matter, and the collider experiments such as the LHC.

  • 14 September 2021, Alejandro Vaquero (University of Utah) -- online slides

    Probing the Standard Model with flavor physics: an exclusive determination of $|V_{cb}|$ from the $B \to D^\ast \ell \nu$ semileptonic decay at non-zero recoil

    A very rich place to look for phenomena to challenge our current understanding of physics is the flavor sector of the Standard Model (SM). In particular, the $V_{cb}$ matrix element of the CKM matrix is the subject of a long standing tension, depending on whether it is determined using inclusive or exclusive methods. On top of that, the current average of $R(D^\ast)$ shows a 3$\sigma$ tension between experiment and the SM calculations. Theoretical support is urgently needed, and in this work I present the first unquenched lattice QCD calculation of the form factors for the decay $B\to D^\ast\ell\nu$ at non-zero recoil. After the form factors are extrapolated from lattice data to the physical point and the continuum limit in the small recoil range, these are extended to the whole kinematic range by using a model-independent parametrization. Comparison with current experimental results coming from Belle and BaBar follows, as well as a joint fit to extract the matrix element $|V_{cb}|$. The lattice prediction for the differential decay rate can be integrated to determine $R(D^\ast)$ using only lattice data.

  • 21 September 2021, Sampsa Vihonen (Sun Yat-Sen University) -- online slides

    Exploring non-standard neutrino interactions in SMEFT with laboratory experiments

    Neutrino oscillation physics is about to enter an era of precision measurements. Next-generation experiments such as DUNE in United States, T2HK in Japan and JUNO in China will measure three-neutrino oscillations at an unprecedented precision and launch the first efficient probes to New Physics in neutrino sector. In this seminar, we discuss how the absence of new particle discoveries in the LHC motivates us to use the recently-developed effective field theory approach in neutrino experiments. We explore how New Physics with high-energy origin could affect neutrino oscillations in accelerator and reactor-based experiments such as the aforementioned DUNE, T2HK and JUNO. We also take a look at coherent elastic neutrino-nucleus scattering in COHERENT and discuss its complementarity to oscillation experiments. Our extensive study illuminates how neutrino experiments can complement, compete and sometimes even outperform other experimental techniques, thus taking us a step towards a more complete picture of physics beyond the Standard Model.

  • 28 September 2021, Istvan Vona (Wigner) slides

    Exact finite volume expectation values of conserved currents

    There are very few local operators even in 1+1 dimensional integrable quantum field theories, whose matrix elements we exactly known between finite volume multiparticle states. Although the expression of the expectation values of higher spin charges was well known, the very different-looking formula for the corresponding current densities was only derived recently in integrable spin-chains. Starting from the vacuum expectation values of conserved currents, one can derive a formula for excited state expectation values by simple analytic continuation, using only some techniques developed in the Thermodynamical Bethe Ansatz framework. The result also takes those non-trivial virtual processes into account, whose presence causes the usual, exponentially suppressed finite-volume corrections in the quantum field theory case.

  • 5 October 2021, Gabor Somogyi (Wigner) slides

    Determination of the strong coupling beyond NNLO

    The strong coupling is a fundamental parameter of the Standard Model and its numerical value at a given scale is a basic constant of Nature. This value can be determined by fitting theoretical predictions to measured data for a wide variety of observables. Clearly the uncertainty of such extractions depends not only on the experimental uncertainties, but also on the accuracy of the theoretical modeling. In this talk, I concentrate on measurements of the strong coupling in electron-positron collisions. I first present a recent determination of the strong coupling from the two-jet rate based on N3LO+NNLL accurate theoretical predictions for this quantity. Then I examine how future measurements might be made even more precise and attempt to identify the factors that are the current main limitations to increased precision. To do so, I present a study of event shape averages in which unknown higher-order perturbative corrections beyond NNLO are estimated from data.

  • 12 October 2021, Gabor Takacs (BME) slides

    Collapse instability and staccato decay of oscillons in various dimensions

    Oscillons are long-lived, slowly radiating solutions of nonlinear classical relativistic field theories. Recently it was discovered that in one spatial dimension their decay may proceed in "staccato" bursts. Here we perform a systematic numerical study to demonstrate that although this behaviour is not confined to one spatial dimension, it quickly becomes unobservable when the dimension of space is increased, at least for the class of potentials considered here. To complete the picture we also present explicit results on the dimension dependence of the collapse instability observed for three-dimensional oscillons. Based on arXiv:2105.01089

  • 19 October 2021, Gergely Barnafoldi (Wigner) slides

    Understanding Underlying Event

    We present a study of the transverse momentum spectra and their evolution in function of the position of the azimuthal of the particles associated to the leading particle. Additionally, the behavior of the spherocity distribution in the same azimuthal bins is reported. The studies were made using proton-proton collisions at s = 13 TeV using PYTHIA8 Monte Carlo event generator. The Multiplicity and midrapidity transverse momentum spectra of charged hadrons have been analyzed in the non-extensive statistical framework. The results on the findings corresponding to the Underlying Event are reported.

  • 2 November 2021, Yoshikazu Nagai (ELTE)

    NA61/SHINE Experiment: Hadron Production Measurements for Neutrino Experiments

    A precise prediction of the neutrino flux is a key input for accelerator-based neutrino experiments. Neutrino beams are created from the decays of secondary hadrons produced in hadron-nucleus interactions. Hadron production is the leading systematic uncertainty source on the neutrino flux prediction; therefore, its precise measurement is essential.

    The neutrino program of the NA61/SPS Heavy Ion and Neutrino Experiment (the NA61/SHINE experiment) at the CERN SPS makes measurements of production of secondary hadrons. In this talk we will present recent hadron production measurements for precise neutrino flux predictions needed by T2K and Fermilab long-baseline neutrino experiments. We will also discuss the prospects for future hadron production measurements with the upgraded NA61 detector and low-energy hadron beamline possibility to extend physics program at NA61/SHINE near future.

  • 9 November 2021, Gyorgy Baranka (ELTE) slides

    Localisation of Dirac modes in finite temperature Z_2 and Z_3 gauge theories on the lattice

    The low-lying Dirac modes become localised at the finite-temperature transition in QCD and in other gauge theories, suggesting a general connection between their localisation and deconfinement. This connection can be understood in terms of the ``sea/islands'' picture of localisation: in the deconfined phase, ``islands'' of fluctuations in the ``sea'' of ordered Polyakov loops, aligned to 1, correspond to ``potential wells'' that trap the eigenmodes, and become deeper as the local Polyakov loop fluctuates farther from 1.

    The simplest model where the connection between localisation and deconfinement and the ``sea/islands'' picture can be tested is Z_2 gauge theory in 2+1 dimensions. I show that in this model the low modes in the staggered Dirac spectrum are delocalised in the confined phase and become localised in the deconfined phase. I also show that localised modes correlate with disorder in the Polyakov loop configuration, in agreement with the ``sea/islands'' picture of localisation, and with negative plaquettes.

    As a further test of the ``sea/islands'' picture, I discuss Z_3 gauge theory in 2+1 dimensions. This model is characterised by the shallowest ``potential wells'', which could prevent localisation of the low modes. Nonetheless, preliminary results show that localisation is present in the deconfined phase, thus further supporting the conjecture that it is closely related with deconfinement.

  • 16 November 2021, Gabor Biro (Wigner) slides

    Studying hadronization with Machine Learning techniques and event variables

    In recent years, the number of Machine Learning applications in high-energy physics has been rapidly increasing. Modern hardwares and software solutions provide a new and powerful tool to study high-energy physics phenomena in an efficient and novel way.

    Hadronization is a non-perturbative process, whose theoretical description requires several assumptions and various phenomenological approaches. However, utilizing state-of-the-art computer vision and deep learning algorithms, it is eventually possible to train neural networks to mimic the behavior of the widely used Lund string fragmentation model. In this pilot study, the first preliminary results of such a neural network is presented, via the comparison of event shape and kinematic observables.

  • 23 November 2021, Daniel Nogradi (Eotvos) slides

    The flavor number and gauge group dependence of m_V / f_PS

    A gauge theory coupled to massless fermions is determined by the gauge group G, the number of flavors Nf and the representation R in which the fermions transform. If the gauge theory is thought to describe a composite Higgs model, where the Higgs boson is identified with the flavor singlet scalar meson, the physical scale is determined by the pseudo-scalar decay constant f_PS = 249 GeV. The mass of m_V (vector meson) in f_PS units determines the mass of the first new, so far unobserved, particle predicted by these class of models. Lattice results will be shown with G=SU(3), Nf=2,3,4,5,6,7,9,10 and R=fundamental in the chiral-continuum limit and surprisingly no statistically significant Nf dependence will be observed.

    A compilation of results from the literature with various G, Nf, R will also be reported for comparison, as well as the expectations from large-N scaling with G=SU(N).

  • 30 November 2021, Niko Koivunen (Tallinn) slides

    Higher spin particles: theory and phenomenology

    A new formulation for higher spin effective theories has recently been developed. This new formalism is dubbed "the multispinor formalism". The multispinor formalism does not introduce unphysical degrees of freedom and thus avoids inconsistencies that often appear in other field theoretical descriptions of higher spin. This is a useful reformulation of Weinberg's original idea but does not allow for Lagrangian description. Multispinor framework has recently been applied to describe dark matter composed of higher spin particles.

    The framework has also been used to study higher spin particles in the high energy colliders where they exhibit rich phenomenology. Higher spin nucleon resonances are well known examples of higher spin particles (albeit not elementary) in nature. The nucleon resonances can also be described by multispinor formalism, as was recently demonstrated. This talk outlines the common problems related to theories of higher spin and presents the new multispinor formalism that is an attempt to alleviate those problems. Finally phenomenological applications of multispinor formalism are presented in context of higher spin dark matter, collider phenomenology and nuclear physics. This talk is based on articles: 2010.02224 [hep-ph], 2102.13652 [hep-ph], 2104.03231 [hep-ph] and 2106.09031 [hep-ph].

  • 7 December 2021, Matteo Giordano (Eotvos) slides

    Localised Dirac eigenmodes at the Roberge-Weiss transition

    Ample numerical evidence from lattice calculations shows a strong connection between localisation of the low-lying Dirac eigenmodes and deconfinement in gauge theories at finite temperature. In this talk I discuss this issue in QCD at imaginary chemical potential mu_I / T = pi at temperatures above the Roberge-Weiss transition temperature T_RW. The Roberge-Weiss transition is a genuine phase transition in a system with dynamical fermions that survives the continuum limit, a setup where the relation between localisation and deconfinement had not been previously investigated. I show that in the high-temperature, deconfined phase above T_RW, modes are localised up to a temperature-dependent "mobility edge", that extrapolates to zero at a temperature compatible with T_RW. This further supports the very close, but not yet fully understood, connection between localisation and deconfinement.

  • 14 December 2021, Sho Iwamoto (Eotvos)

    Explore beyond the Standard Model

    In this colloquium-like talk, I will provide an overview of the main theme of our phenomenology group, i.e., the exploration for beyond-the-Standard-Model physics. Starting from a very basic review of the field, I will introduce what we are actually doing in our research and discuss two scenarios as examples: SUSY (as my primary interest) and the "superweak scenario" (as of interest of the group). Although you may have heard related talks from me and the group members, this talk is designed for pedestrians and may help you understand our research activities.

  • 11 January 2022, Kare Fridell (Technical University Munich) slides

    Probing neutrino masses and baryogenesis using low- and high-scale observables

    The Standard Model (SM) is a highly successful theory, however there are some strong motivations to go beyond it. Two of these are neutrino oscillations, which implies that neutrinos have a non-zero mass, and the observed matter/antimatter asymmetry of the Universe, which can be generated dynamically by a mechanism known as baryogenesis. In many models, both of these phenomena are explained using high-scale physics that can be outside the reach of current experiments. In this talk I will discuss three interesting observables: coherent elastic neutrino-nucleus scattering, neutron-antineutron oscillations, and rare kaon decays, and how they can probe the nature and mass mechanism for neutrinos and baryogenesis using an effective field theory approach as well as simplified models.

  • 17 January 2022 (Monday), Krzysztof Jodlowski (National Center for Nuclear Research, Warsaw)

    Signatures of light dark matter and long-lived particles at the LHC and in space

    The Large Hadron Collider found no clear evidence for new electroweak-scale physics except for the Higgs boson. This places quite severe constraints on weakly interacting massive particles - one of the main frontier in experimental and theoretical studies of physics beyond the Standard Model - and prompts consideration of other well-motivated, but less constrained possibilities. Among them, light new physics emerged as a particularly active research direction, since such particles could naturally answer many pressing problems of particle physics and cosmology, while avoiding detection in the past due to incomplete dedicated experimental coverage. I will discuss several aspects of light BSM physics, focusing on forward physics program at the LHC to be initiated with the FASER experiment. I will illustrate it for GeV-scale heavy neutral leptons that could be produced in neutrino scatterings mediated by the dipole or light vector portal, and also for long-lived dark photons, dark Higgs bosons, and stable dark matter particles of similar masses that can be produced in interaction directly in front of the detector. We find that such secondary production of new physics species will extend the reach of FASER and the proposed MATHUSLA and SHiP detectors towards shorter lifetimes, a regime important for explaining various anomalies, e.g. the (g-2) muon anomaly. Time permitting, I will also discuss cosmological impact of long-lived particles.

  • 24 January 2022, Amy Schertz (College of William & Mary)

    Searching for Exotic Mesons in the omega-pion System At GlueX

    The meson has traditionally been understood as the bound state of a quark and an antiquark, but there is experimental evidence for exotic meson states, which have properties that cannot be produced by this quark-antiquark model. This talk will outline several possible exotic structures, with a focus on the hybrid meson, which includes gluonic excitation in its wavefunction. We will then discuss the search for hybrids at GlueX, a photoproduction experiment at Jefferson Lab in Newport News, Virginia, USA, and the role that analysis of the omega-pion decay channel plays in that search.

  • 26 January 2022 9AM, Sayan Ghosh (Saha Institute of Nuclear Physics)

    Investigations on some physics issues and experimental aspects of Dark Matter Search

    Through various astrophysical and observational evidence, we know that almost 26.8% of the universe is made up of an unknown, non-luminous form of matter known as Dark Matter (DM). In this presentation, I shall cover some aspects of indirect and direct detection of dark matter. In this context, I shall discuss the formulation of a particle physics DM model to examine the viability of explaining the positron excess data of AMS-02 from the point of view of DM annihilation. In the avenue of direct DM search, I shall cover some developmental aspects of setting up a new DM direct detection experiment in India. In this respect, I shall present background radiation measurements at a 555 m deep underground site identified for this experiment. In addition, I shall also show some initial characterization results of photon-readout devices, the Silicon Photomultipliers, and some doped and un-doped scintillators at low temperatures to identify the most suitable detector for DM search in India. Finally, I shall also discuss the possibility of using large volume liquid Xenon-based dual-phase TPCs, primarily designed for DM search, for Supernova neutrino detection.

  • 27 January 2022 9AM, Kanishka Rawat (Saha Institute of Nuclear Research)

    Neutrino Simulation and Geant4-based Studies with Different Sources

    The proposed magnetized Iron CALorimeter (ICAL) at India-based Neutrino Observatory (INO) aims to study atmospheric neutrinos and their properties [1]. The work was focused on detector development and simulations. The fabrication and characterization of scintillators and active detectors i.e., resistive plate chambers (RPCs) has been done. The ICAL has three different regions namely the central, peripheral and side regions based on the magnitude and direction of the magnetic field in the detector. The work also involved geant4-based simulation studies of muons in the central as well as the peripheral and side regions of the detector. The muon response (resolutions and efficiencies) in all the regions (central, peripheral, side) of the ICAL detector have been studied and compared [2, 3]. The study of muons in the peripheral regions were done specifically for their application in determining the oscillation sensitivity and precision measurements on sin^2(theta_23), Delta m^2_32 using upward-going muons in ICAL detector for 10 years. Upward-going muons come from the interactions of atmospheric neutrinos with the rock material surrounding the detector within ~200 m. The oscillation sensitivity of atmospheric muons and upward-going muons were combined. Hierarchy sensitivity for the combined analysis (atmospheric muons and upward-going muons) has been done too.

    A geant4-based simulation study was done to find the photon collecion efficiency of ARAPUCA and X-ARAPUCA which is a novel concept for liquid argon scintillation light detection, proposed for the photon detection system at DUNE [4].

    In many particle physics experiments, the primary ionization is utilized in understanding the charge density and discharge formation studies. We present the simulation of primary ionization in argon based gas mixtures to get the number of primaries, energy and spatial information with geant4 and heed++ that have been used to simulate the passage of particles through the matter. The geant4 toolkit has an advantage of obtaining the particle information like energy deposition and position co-ordinates after each step even in a complex, realistic, three-dimensional geometry. These steps generate each interactions after computing the cross-sections of physics processes that were taken into account for this simulation in a gas volume. Alpha and muons were simulated to study the primary ionization [5]. A similar study of primary ionization was carried out with 55Fe which is a radioactive source. 55Fe captures an electron to form 55Mn (X-rays), nu_e, auger electrons and gamma in this process. A new simulation study using NPTool has also been started for low energy reactions in TPC. These reactions will be carried out as per the beam availability at FRENA (Facility for Research in Experimental Nuclear Astrophysics).

    References:

    [1] Invited review : Physics potential of the ICAL detector at the India-based Neutrino Observatory (INO), Kumar A., Vinod Kumar A.M., Jash A., et al. , Pramana J Phys 88 (2017).

    [2] A Simulations Study of the Muon Response of the Iron Calorimeter detector at the India-based Neutrino Observatory, A. Chatterjee, K.K. Meghna, R. Kanishka, T. Thakore et al., JINST 9 P07001 (2014).

    [3] Simulations study of muon response in the peripheral regions of the Iron Calorimeter detector at the India-based Neutrino Observatory, R. Kanishka et al., JINST 10 P03011 (2015).

    [4] ARAPUCA a new device for liquid argon scintillation light detection, A.A. Machado and E. Segreto, JINST 11 C02004 (2016).

    [5] Numerical estimation of discharge probability in GEM-based detectors, P. K. Rout, R. Kanishka et al, JINST 16 P09001 (2021).

  • 22 February 2022, Feiyi Liu (Eotvos)

    A Transfer Learning Method to Phase Transitions

    The latest advances of statistical physics have shown remarkable performance of machine learning in identifying phase transitions. Currently, we apply domain adversarial neural network (DANN) based on transfer learning to study non-equilibrium and equilibrium phase transition models, namely a 2d percolation and a (1+1)d directed percolation (DP) model, respectively. With the DANN, only a small fraction of input configurations (2d images) need to be labeled, which can even be done automatically, to capture the critical point. In order to enhance the performance, we introduce an iterative procedure to determine the critical point. From here, using data collapse the critical exponent nu_perp follows. Next, we apply the DANN to a two-dimensional site percolation with configurations filtered to include only the largest cluster, the information related to the order parameter. The DANN learning of both models yields reliable results which are comparable to the ones from Monte Carlo simulations. Our study also shows that the DANN can achieve quite high accuracy at much lower cost, compared to the supervised learning.

    The related paper is arXiv:2112.15516

  • 22 March 2022, Zoltan Tulipant (Eotvos) slides

    Ameliorating the sign problem in 2+1D XY model at non-zero chemical potential

    The simulation of euclidean quantum field theories at non-zero chemical potential is generally hampered by a complex action problem. The path integral weights take complex values and are no longer suitable to be used directly as probability weights. This difficulty can be overcome by performing simulations using the absolute value of the integrand as a weight in importance sampling and then reweighting to the theory of interest. This approach, however, is severely restricted by a sign problem which causes uncertainties to increase exponentially in both the volume and the chemical potential. One way to alleviate the sign problem is to deform the integration manifold of the path integral. This method has already shown promising results. We studied the 2+1 dimensional XY model at non-zero chemical potential and investigated several proposals for deformations. In this talk I present numerical evidence that a significant reduction of the sign problem can be achieved which is exponential in both squared chemical potential and volume. Furthermore, I discuss a new approach to the optimization procedure that reduces its computational cost.

  • 5 April 2022, Karoly Seller (Eotvos) slides

    Sterile Neutrino Dark Matter in the Super-weak Extension of the Standard Model

    The existence of dark matter (DM) today is a well established experimental fact. However the standard model (SM) of particle physics is unable to provide us with a valid candidate particle for DM. This problem has lead to the possible need of extending the SM. We consider one such extension, the so-called Super-weak model, where the newly added right-handed neutrinos could play the role of DM. We present the relevant characteristics of the model, and discuss the new particle spectrum and interactions. After this introduction we discuss dark matter production in general, focusing on the freeze-in and freeze-out scenarios. Once these scenarios are applied to the Super-weak model, we find that the lightest sterile neutrino is a valid DM candidate with a non-vanishing parameter space. Finally, experimental constraints coming from measurements in both particle physics and astrophysics are investigated, and applied to the favored parameter space of our model.

  • 12 April 2022, Istvan Vona (Eotvos)

    Resurgence in the O(N) sigma models

    The two-dimensional O(3) and O(4) non-linear sigma models - in an external magnetic field - were the first where an exact mass-gap relation was calculated in an asymptotically free theory. Integrability leads to an exact solution in terms of a linear integral equation here, and an effective algorithm by Volin provides us high-order perturbative coefficients of physical quantities in terms of the running coupling in the large magnetic field regime. As usual, these coefficients are growing factorially, leading to an asymptotic series with zero radius of convergence. However, the theory of resurgence gives us hints at how to reconstruct the correct dependence of these quantities on the coupling, which also contains exponentially suppressed terms besides the perturbative series. One can test these predictions by comparing them to a high-precision numerical solution of the integral equation. In the case of the O(4) model, there is a complete agreement between the prediction and the numerics, whereas in the case of the O(3) the observed discrepancy can be explained by analyzing the integral equation using the Wiener-Hopf method. As the integral equation for the O(3) model - by accident - also describes the disk capacitor problem in classical electrodynamics; the same techniques can be used to analyze the appearing resurgent structures in these related models as well. The aim of the talk is a brief introduction to these techniques and a short summary of the results.

  • 26 April 2022, Eszter Frajna (Wigner) slides

    Heavy-flavour correlation measurements with the ALICE experiment

    Measurements of heavy-flavor quarks provide essential information on the properties of the strongly interacting system formed in the early stages of heavy-ion collisions at very high energy density. Heavy quarks (charm and beauty) are produced in the early stages of the reaction and live long enough to interact with the medium. The unique particle identification capabilities of the ALICE experiment allow for precise evaluation of such probes at LHC energies. Heavy-flavor production in proton-proton collisions can be used as a test for perturbative QCD models as well as to understand parton fragmentation into jets, while in heavy-ion collisions, radiative and collisional parton energy loss mechanisms can be investigated. In the future, ALICE3, which is a next-generation heavy-ion experiment for LHC Run 5, will provide unique access to this topics and open up new possibilities in other areas.

    In this talk we will give an overview of azimuthal angle correlations with ALICE experiment at the LHC. The measurement of of charm particles at mid-rapidity provides unique information on the formation of jets. In the future, ALICE3 will aid to understand the connection between heavy quark transport and hadronisation and one such example is the measurement of azimuthal correlations between charm and anti-charm mesons.

  • 7 June 2022, Janos Polonyi (Strasbourg) slides

    Renormalizing open quantum field theories

    Quantum field theories are always treated by a two step process owing to the inherent UV divergences: First the infinities are regulated by the introduction of a cutoff which is placed far away from the scale of observations and reflects our ignorance of physics. Next the physical content is made independent of the choice of the cutoff by using cutoff-dependent parameters in the action. The retained IR degrees of freedom interact with the unobserved UV particle modes hence quantum field theories are open by definition and their vacuum state is always mixed.

    Open interaction channels introduce new parameters and some of them are renormalizable according to power counting. However the removal of the cutoff meets other conditions beyond such a simple dimensional argument. A new phase is located in open 1+3 dimensional scalar field theory with strong, non-perturbative IR-UV entanglement which casts shadow on the usual quantization rules based on classical physics.

  • 13 September 2022, Gergely Barnafoldi (Wigner) slides

    Estimating elliptic flow coefficient in heavy ion collisions using deep learning

    Machine learning techniques have been employed for the high energy physics community since the early 80s to deal with a broad spectrum of problems. This work explores the prospects of using deep learning techniques to estimate elliptic flow (v2) in heavy-ion collisions at the RHIC and LHC energies. A novel method is developed to process the input observables from particle kinematic information. The proposed deep neural network (DNN) model is trained with Pb-Pb collisions at sNN=5.02 TeV minimum bias events simulated with a multiphase transport model. The predictions from the machine learning technique are compared to both simulation and experiment. The deep learning model seems to preserve the centrality and energy dependence of v2 for the LHC and RHIC energies. The DNN model is also quite successful in predicting the pT dependence of v2. When subjected to event simulation with additional noise, the proposed DNN model still keeps the robustness and prediction accuracy intact up to a reasonable extent.

    N. Mallick et al: Phys.Rev. D105 (2022) 11, 114022

  • 20 September 2022, Gabor Etesi (BME) slides

    The universal von Neumann algebra of smooth four-manifolds

    Making use of its smooth structure only, out of a connected oriented smooth 4-manifold a von Neumann algebra is constructed. As a special four dimensional phenomenon this von Neumann algebra contains algebraic (i.e., formal or coming from a metric) curvature tensors of the underlying 4-manifold and the von Neumann algebra itself is a hyperfinite factor of type II_1 hence is unique up to abstract isomorphisms of von Neumann algebras. Over a fixed 4-manifold this universal von Neumann algebra admits a particular representation on a Hilbert space such that its unitary equivalence class is preserved by orientation-preserving diffeomorphisms consequently the Murray--von Neumann coupling constant of this representation is well-defined and gives rise to a new and computable real-valued smooth 4-manifold invariant. Its link with Jones' subfactor theory is noticed as well as computations in the simply connected closed case are carried out.

    Application to the cosmological constant problem is also discussed. Namely, the aforementioned mathematical construction allows to reformulate the classical vacuum Einstein equation with cosmological constant over a 4-manifold as an operator equation over its tracial universal von Neumann algebra such that the trace of a solution is naturally identified with the cosmological constant. This framework permits to use the observed magnitude of the cosmological constant to estimate by topological means the number of primordial black holes about the Planck era. This number turns out to be negligable which is in agreement with known density estimates based on the Press--Schechter mechanism.

    Based on this preprint.

  • 27 September 2022, Timea Vitos (Lund University) slides

    Improving on accuracy and efficiency of Standard Model theory predictions

    In the process of improving experimental accuracy at the LHC and other colliders, it is essential that theory predictions keep up this pace. Specifically, in the search of theories beyond the Standard Model, it is crucial to have a very precise handle on what this successful model actually predicts. This task consists of using the existing tools for various key observables, and also to improve on the scope and efficiency of the tools. In this talk, three important LHC processes and corresponding spin-related observables at NLO electroweak precision are presented: Z+jet, W+jet (also including NNLO QCD) and top-antitop pair production. In addition, the first steps towards a more efficient approach to handle high-multiplicity jet processes is presented, via the next-to-leading colour approximation of the colour matrix.

  • 4 October 2022, Zoltan Peli (ELTE) slides

    Vacuum stability and scalar masses in the superweak extension of the standard model

    We study the allowed parameter space of the scalar sector in the superweak extension of the standard model (SM). The allowed region is defined by the conditions of (i) stability of the vacuum and (ii) perturbativity up to the Planck scale, (iii) the pole mass of the Higgs boson falls into its experimentally measured range. The method can be generalized in a straightforward way to simpe beyond the standard model scenarios such as the singlet scalar extension. We confront our findings against the measured mass of the W boson and the measured width of the Higgs boson. Preliminary results for collider search constraints are also shown.

  • 11 October 2022, Rachel Houtz (Durham IPPP) slides

    Hamiltonian Truncation Effective Theory

    Hamiltonian truncation is a non-perturbative numerical method for calculating observables of a quantum field theory. In this talk, I will show how to treat Hamiltonian truncation systematically using effective field theory methodology. The starting point for this method is to truncate the interacting Hamiltonian to a finite-dimensional space of states below some energy cutoff Emax. The effective Hamiltonian can be computed by matching a transition amplitude to the full theory, and gives corrections order by order as an expansion in powers of 1/Emax. This method is demonstrated using 2D lambda phi^4 theory, and gives 1/Emax^2 corrections to the effective Hamiltonian. Numerical diagonalization of the effective Hamiltonian then shows residual errors of order 1/Emax^3, as expected by our power counting.

  • 18 October 2022, Miklos Vincze (ELTE) slides

    Modeling atmospheric and ocean dynamics in the lab

    Based on the principle of hydrodynamic similarity many fundamental aspects of Earth's climate system can be modeled using laboratory-scale experimental set-ups. Under laboratory conditions it is possible to control the governing physical parameters and thus to separate different processes that cannot be studied independently in such complex systems as the real atmosphere or oceans. In our research at the von Karman Laboratory for Environmental Fluids of our institute and similar research facilities around the world we have investigated climate dynamics-motivated problems focusing on the transitions between different states of "minimal models" of the mid-latitude atmospheric and ocean circulation, shedding light on the processes that had yielded the formation of permanent ice cover on Antarctica 34 million years ago, the distribution of extreme temperature fluctuations in a changing climate, and various forms of atmospheric fluid dynamic instabilities.

  • 25 October 2022, Andras Laszlo (Wigner) slides

    On generally covariant mathematical formulation of Feynman integral in Lorentz signature

    Feynman integral is one of the most promising methodologies for defining a generally covariant formulation of nonperturbative interacting quantum field theories (QFTs) without a fixed prearranged causal background. Recent literature indicates that in such scenario, one needs to consider the problematics in the original Lorentz signature. Lorentz signature Feynman integrals are known, however, to be mathematically ill-defined. The Feynman integral formulation has, however, a differential reformulation: the master Dyson-Schwinger (MDS) equation for field correlators. In this talk we show that with the right choice of variables, the MDS equation is mathematically well defined: the involved function spaces and operators can be defined and their properties can be established. Therefore, MDS equation can serve as a substitute for the Feynman integral, in a mathematically sound formulation of constructive QFT, in arbitrary signature, without a fixed background causal structure. It is also shown that the Wilsonian regularization of the MDS equation can be canonically defined. Our main result is a necessary and sufficient condition for the regularized MDS solution space to be nonempty, which also provides a convergent iterative approximation for the solution. The talk is based on the paper: Class.Quant.Grav.39(2022)185004.

  • 15 November 2022, Gergely Fejos (ELTE) slides

    Thermal fate of the U_A(1) anomaly from the functional renormalization group

    I will review some recent results regarding the finite temperature behavior of the axial anomaly. Using the functional renormalization group technique, I will show how to effectively resum an infinite class of anomaly breaking operators in the framework of the three flavor meson model. The resulting condensate dependent anomaly coupling shows that mesonic fluctuations actually strengthen the U_A(1) breaking toward the pseudocritical temperature, which are to be compared with the effects of the instantons. Numerics suggest that there is an intermediate region below T_c, where the former can become the dominant factor. If time permits I will also challenge some old results concerning the order of the chiral transition for massless quarks, which, surprisingly, may also be strongly related to the thermal fate of the axial symmetry.

    Based on G. Fejos and A. Patkos, Phys. Rev. D105, 096007 (2022) and G. Fejos, Phys. Rev. D105, L071506 (2022)

  • 29 November 2022, Dimitrios Bachtis (Paris, Ecole normale superieure) slides

    Machine learning and the inverse renormalization group

    Standard renormalization group methods iteratively eliminate degrees of freedom within a system and are therefore applicable for a limited number of steps before the degrees of freedom vanish. In this talk I will present the construction of inverse renormalization group transformations with the use of machine learning. Inverse renormalization group transformations enable the generation of configurations for increasing lattice size in absence of the critical slowing down effect and can, in principle, be applied for an arbitrary number of steps. I will additionally discuss the interpretation of machine learning functions as physical observables to introduce a Hamiltonian-agnostic reweighting approach, and the inclusion of neural networks within Hamiltonians to break or restore the symmetry of a system without any knowledge of the system's order parameter. Applications will be presented based on the phi^4 theory and the Ising model, with an emphasis on the calculation of multiple critical exponents and the critical fixed point.

  • 7 March 2023, Gyozo Kovacs (Wigner) slides

    Fate of the critical endpoint at large Nc

    The phase diagram of QCD is investigated by varying number of colors Nc within a Polyakov loop quark-meson chiral model. In particular, our attention is focused on the critical point(s); the critical point present for Nc=3 moves toward the mu_q-axis and disappears as soon as the number of color is increased. Yet, a distinct critical point emerges along the temperature axis for Nc=53 and moves toward finite density when increasing Nc further. Thus, the phase diagram at large Nc looks specular with respect to the Nc=3 results, with the first-order transition in the upper-left and crossover in the lower-right regions of the (mu_q,T)-plane. The pressure is also evaluated in dependence of Nc, showing a scaling with Nc^0 in the confined and chirally broken phase and with Nc^2 in the deconfined one. Moreover, the presence of a chirally symmetric but confined "quarkyonic phase" at large density and moderate temperature with a pressure proportional to Nc is confirmed.

  • 14 March 2023, Balazs Pozsgay (Eotvos)

    Exotic symmetries and breakdown of ergodicity from hard rod deformations

    We treat a new mechanism for ergodicity breaking in one dimensional quantum many body systems. We treat spin chains with local Hamiltonians, which have a special fine tuned form: there is interaction in the system, nevertheless the models have a large non-commutative symmetry algebra, generated by Matrix Product Operators (MPO). Meanwhile, the models are NOT integrable, and not exactly solvable. The exotic symmetries cause exact degeneracies in the finite volume spectrum, leading to a breakdown of thermalization. The mechanism we treat is a special type of ,,Hilbert space fragmentation''. It appears that our models are the first ones, where non-commutative MPO symmetries are found, such that the models are not integrable.

  • 21 March 2023, Mate Lencses (Wigner) slides

    Multicriticality in Yang--Lee edge singularity

    The Yang--Lee edge singularity is related to the anomalous behaviour of zeroes of the partition function in the two-dimensional Ising model. It was shown by Cardy, that this behaviour is described by the M(2,5) nonunitary minimal model of conformal field theory, known as the Yang--Lee model. This model can be realised as the Ising model above the critical temperature in an imaginary external magnetic field, as the point where the PT symmetry becomes spontaneously broken. In this talk, I will consider the analogue of this scenario in the tricritical Ising model, where a three-parameter family of nonunitary PT-symmetric flows exists. I will present our findings regarding massless flows ending in the Yang--Lee model and in a nonunitary "tricritical" point identified as M(2,7). Finally, I will discuss our conjecture on higher nonunitary multicritical points, connected by PT-symmetric nonunitary flows.

  • 28 March 2023, Arthur Hutsalyuk (Eotvos) slides

    Finite temperature spin diffusion in the Hubbard model in the strong coupling limit

    We investigate finite temperature spin transport in one spatial dimension by considering the spin-spin correlation function of the Hubbard model in the limiting case of infinitely strong repulsion. We find that in the absence of bias the transport is diffusive, and derive the spin diffusion constant. Our approach is based on asymptotic analysis of a Fredholm determinant representation, which is entirely analytic and free of phenomenological assumptions of Generalized Hydrodynamics.

    Based on arXiv:2301.13840, O. Gamayun et. al.

  • 4 April 2023, Zoltan Bajnok (Wigner) slides

    The full analytic trans-series in integrable field theories

    We analyze a family of generalized energy densities in integrable quantum field theories in the presence of an external field coupled to a conserved charge. By using the Wiener-Hopf technique to solve the linear thermodynamic Bethe ansatz equations we derive the full analytic trans-series for these observables in terms of a perturbatively defined basis. We show how to calculate these basis elements to high orders analytically and reveal their complete resurgence structure. We demonstrate that the physical value of the generalized energy densities is obtained by the median resummation of their ambiguity-free trans-series.

  • 11 April 2023, David Pesznyak (Eotvos) slides

    Fighting the sign problem in a chiral random matrix model with contour deformations

    First principle studies of Euclidean quantum field theories at finite chemical potential are hindered by the so-called complex action problem, i.e. the Boltzmann weights of the path integral cannot be regarded as a probability density function. Upon reweighting from an appropriately modified theory the complex action problem reduces to the sign problem: cancellations in the sampled data lead to small signal-to-noise ratios in the expectation values of observables. The sign problem is present in a number of theories, e.g. QCD at finite baryon density or the Hubbard model away from half-filling. Our goal is to ameliorate the severity of the sign problem through complex integration contour deformations in the path integrals. In the presented work we study the chiral random matrix theory of Stephanov - a toy model of QCD at finite baryochemical potential - which also has a sign problem. We studied integration contour deformations with simple ansatze and optimized their parameters with machine learning techniques. Furthermore, we also investigated contour deformations via the holomorphic flow equations, which is an alternative way to obtain integration manifolds with a less severe sign problem. Our findings show that the optimization of a single parameter leads to a considerable improvement in the severity of the sign problem, and that it is also exponential in the degrees of freedom of the system.

  • 25 April 2023, Karoly Seller (Eotvos)

    Real effective potentials for phase transitions in models with extended scalar sectors

    The effective potential obtained by loop expansion is usually not real in the range of field values explored by its minima during a phase transition. The appearance of complex values is due to the breakdown of conventional perturbation theory when applied to a non-convex classical potential. To solve this issue, we apply the "optimized perturbation theory" in a fixed gauge to the SM, and singlet scalar extensions of it, in order to calculate a one-loop effective potential that is real by construction. We test this computational scheme by comparing such a potential obtained in Landau gauge to that derived based on the Higgs pole mass.We use our effective potential to study the parameter dependence of the critical temperatures in a two-step phase transition of the form (0,0) -> (0,w') -> (v,w) that occurs for decreasing temperature in scalar extensions of the SM with two non-zero vacuum expectation values v and w.

  • 2 May 2023, Tamas Gy Kovacs (Eotvos)

    Chiral symmetry, instantons and the Dirac spectrum in hot QCD

    The spectrum of the QCD Dirac operator encodes important information about the physical properties of strongly interacting systems. In particular, the lowest part of the spectrum is strongly related to the spontaneously and anomalously broken chiral symmetries and their possible restoration in the quark-gluon plasma phase. In contrast to standard lore, above the transition temperature the spectral density at zero does not vanish, but it develops a pronounced peak that is presently extensively discussed in the literature because of its influence on chiral symmetry restoration. I will show that the spectral peak can be understood based on a dilute gas of instantons and antiinstantons. Hopefully this simple picture can be used to determine the behavior of the spectral peak in the thermodynamic limit and the chiral limit, two limits that are extremely hard to access directly by using lattice simulations.

  • 9 May 2023, Janos Takatsy (Wigner) slides

    What neutron stars tell about the hadron-quark phase transition

    The low temperature - high density part of the phase diagram is yet only accessible through observations of neutron stars. The existence of quark matter inside the heaviest neutron stars has been the topic of numerous recent studies, many of them suggesting that a phase transition to strongly interacting conformal matter inside neutron stars is feasible. We examine this hybrid star scenario using various hadronic models, an effective constituent quark model with three quark flavours, and applying a smooth crossover transition between the two. We use astrophysical observations in a Bayesian framework to constrain the equation of state and parameters of our quark model and the crossover phase transition. Among other discoveries, we find that a peak in the speed of sound, exceeding the high density, conformal limit, is highly preferred, which might suggest the percolation of hadrons at densities existing in heavy neutron stars.

  • 16 May 2023, Daniel Nogradi (Eotvos) slides

    The f_{PS,V} / m_V ratios and the conformal window

    The mesonic f_PS / m_V and f_V / m_V ratios, with f the decay constant and m the meson mass, are calculated in mass perturbed conformal gauge theories to NNLO and N^3LO orders, respectively. Here NNLO and N^3LO refer to the non-relativistic effective theory expansion which is the applicable framework. The results are expanded a la Banks-Zaks in order to end up with scheme-independent predictions. These perturbative results are unambiguously reliable close to the upper end of the conformal window, Nf = 16.5 and it is shown that they might be reliable down to Nf = 12. An attempt is made to match these to previous non-perturbative lattice results in the range 1 < Nf < 11. An abrupt change in the ratios is observed at around Nf = 12 - 13, which may signal the lower end of the conformal window.

  • 26 September 2023, Zoltan Trocsanyi (Eotvos) slides

    Status of the superweak extension of the standard model

    The superweak force is a minimal, anomaly-free U(1) extension of the standard model, designed to explain the origin of (i) neutrino masses and mixing matrix elements, (ii) dark matter, (iii) cosmic inflation, (iv) stabilization of the electroweak vacuum and (v) leptogenesis. In this talk we discuss the phenomenological status of the model and provide viable scenarios for the physics of the items in this list. The talk is based on the following research articles on the arXiv: 1812.11189 (Symmetry), 1911.07082 (PRD), 2104.11248 (JCAP), 2104.14571 (PRD), 2105.13360 (J.Phys.G), 2204.07100 (PRD), 2301.07961 (JHEP), 2301.06621 (PRD), 2305.11931 (PRDL) and correspondence with the Budapest-Marseille-Wuppertal group, written in collaboration with S. Iwamoto, T.J. Karkkainen, I. Nandori, Z. Peli, K. Seller, Zs. Szep.

  • 3 October 2023, Marton Kormos (BME) slides

    Thermodynamics, transport, and fluctuations in the sine-Gordon model

    The sine-Gordon model is a paradigmatic quantum field theory that provides the low-energy effective description of many gapped 1D systems. Despite this fact, its complete thermodynamic description in all its regimes was lacking. In the talk, I will report the filling of this gap by deriving the Thermodynamic Bethe Ansatz framework that captures the thermodynamics of the model and serves as the basis of its hydrodynamic description. As a first application, I will present results on the Drude weight characterising the ballistic transport of the topological charge and demonstrate that its dependence on the value of the coupling features a fractal structure. I will also show recent results about the large-scale fluctuations of the topological charge and current.

    Based on 2305.10495 and 2305.15474

  • 10 October 2023, Tamas Biro (Wigner) slides

    Hadron Resonances - Quark Matter viewed by nonlinear Regge trajectories

    We review the idea of connecting scattering cross sections and amplitudes with equation of states inside the proton via the hadronic resonance mass spectrum obtained from a nonlinear Regge model with resonance threshold contributions. The last step in the cross section measurement -> amplitude -> reggeon (pomeron, etc) -> mass distribution -> pressure chain can in principle be reversed, and a mass distribution can be associated to the lattice QCD equation of state (pressure - temperature relation) utilizing an inverse Meijer transformation.

  • 17 October 2023, Sergei Maydanyuk (Wigner) slides

    Synthesis of elements in compact stars in pycnonuclear fusion

    Purpose: In the proposed talk possibility of synthesis of nuclei in stellar matter of comact stars (white dwarfs, neutron stars) will be analyzed. Conditions of formation of compound nuclear system needed for synthesis of heavy nuclei in pycnonuclear reactions in compact stars are studied on quantum mechanical basis.

    Methods: As a method for study, new quantum method of high precision and tests (called as Multiple internal reflections) is used. This method is generalized for pycnoreactions in compact stars with new calculations of quasibound spectra and spectra of zero-point vibrations.

    Results: Peculiarities of the method are analyzed for reactions with isotopes of Carbon. The developed method takes into account continuity and conservation of quantum flux (describing pycnonuclear reaction) inside the full spacial region of reaction including nuclear region. High precision of calculations by the method will be demonstrated. This study gives appearance of new states (called as quasibound states), in which compound nuclear systems of Magnesium are formed with the largest probability. These states have not been studied yet by other researchers in study of synthesis of elements in stars. Energy spectra of zero-point vibrations and spectra of quasibound states are estimated with high precision for reactions with isotopes of Carbon.

    Conclusions: Probability of formation of compound nuclear system in quasibound states in pycnonuclear reaction is essentially larger than probability of formation of this system in states of zero-point vibrations studied by Zel'dovich and followers of that idea. Therefore, synthesis of more heavy nuclei of Magnesium from isotopes of Carbon is essentially more probable in quasibound states than in states of zero-point vibrations in compact stars.

  • 24 October 2023, Gyula Fodor (Wigner) slides

    Beyond-all-order effects in a fifth order Korteweg-de Vries equation

    When the Korteweg-de Vries equation is perturbed by a fifth derivative term soliton solutions become weakly localized. Away from the core, the asymptotics of these solutions consist of exponentially small amplitude (beyond-all-orders small) standing wave tails. We present three different methods to calculate the amplitude of these tails, compare the results, and check their domains of validity. The numerical method uses spectral expansion in terms of Chebyshev polynomials, applying more than 16 digits arithmetics in order to resolve the extremely small tail. The second approach is a perturbative scheme that requires extension to the complex plane and asymptotic matching. Not only the leading order result for the amplitude but higher order corrections can also be calculated. The third method is based on the asymmetric solution which is regular and tends to zero on one side of the core, but singular at the other side. The asymmetry at the center of this configuration can be calculated from the analytical solution of Hammersley and Mazzarino, defined by a convergent power series. The difference between the symmetric and the regular part of the asymmetric solutions is sufficiently small so that their difference can be well approximated by a WKB type calculation. This can be used the determine the tail amplitude of the original symmetric solution to a remarkable precision even when it is beyond the capabilities of standard numerical methods.

  • 7 November 2023, Peter Van (Wigner) slides

    Simple holographic fluids: from Newtonian gravity to quantum mechanics

    Non-equilibrium thermodynamics has developed various methods for constructing evolution equations for dissipative processes. In this lecture, I will show, using the examples of Newtonian gravity and Korteweg fluids, that the Second Law of thermodynamics, with correct consideration of Galilean relativistic spacetime and various constraints, determines both the ideal and the dissipative forms of the evolution equations. A general consequence of thermodynamic compatibility is the classical holographic property, i.e. that the volume density can be equivalently written as the divergence of a special constitutive pressure tensor. Further benchmarks are various generalizations of the classical equations, with unexpected physical consequences.

    I will show , that quantum mechanics, superfluids, strongly correlated quantum plasmas, and capillary fluids are closely related: it is thermodynamics that links them. I will also briefly discuss various alternative theories of gravity and interpretational issues of quantum mechanics, with particular reference to recent advances in pilot-wave, Bohmian and fluid formulations.

  • 21 November 2023, Arpad Hegedus (Wigner) slides

    Strong coupling results from the numerical study of the spectrum in planar N=4 super Yang-Mills theory

    Maldacena's famous AdS/CFT correspondence, states that type IIB string theory on AdS5xS5 is equivalent to N=4 super Yang-Mills theory. The integrability discovered on both sides of the correspondence, offers useful and efficient tools to solve these models non-perturbatively in the planar limit. The most efficient such mathematical tool to study the spectrum in the planar limit, is the so-called Quantum Spectral Curve (QSC). In this talk, I shortly review the QSC equations and the strategy for their numerical solution. Then, I summarize, how the numerical results can be used to obtain strong coupling results for the anomalous dimensions and for some special operator product expansion coefficients.

  • 5 December 2023, Joshua Eby (Stockholms Universitet)

    Discovering Ultralight Dark Matter on Earth, Across the Solar System, and Around the Galaxy

    Dark matter is a cornerstone of our understanding of cosmology and astrophysics, yet its particle identity remains unknown. A highly-motivated class of models, known as ultralight dark matter (ULDM), can solve this mystery while providing unique and detectable signals in a broad range of experimental searches. In this talk, I will discuss how the very low masses of ULDM particles give rise to large-scale wave dynamics of dark matter in galaxies. As a consequence, the ULDM field can be amplified by gravitational focusing and Bose enhancement in astrophysical environments, leading to rapid growth of field inhomogeneities which results in large dark matter densities at the position of the Sun, the Earth, and other astrophysical bodies. I will emphasize the consequences for terrestrial, space-based, and astrophysical search prospects (including precision quantum sensors), which are highly complementary in their detection capabilities and can cover large regions of ULDM parameter space.

  • 12 December 2023, Peter Athron (COEPP)

    Predicting gravitational wave spectra from Cosmological phase transitions

    The first observation of gravitational waves (2017 nobel prize for physics) opened up a new window into particle physics as well as astronomy. In particular gravitational waves can be produced from first order cosmological phase transitions that occur early in the Universe. Cosmological phase transitions play a key role in particle physics leading to the Higgs mechanism where electroweak symmetry is broken and the transition from the quark- gluon plasma to confined hadrons such as protons and neutrons. They also appear in many extensions of the standard model of particle physics such as grand unified theories and first order cosmological phase transitions are a vital ingredient in solutions to the matter anti-matter asymmetry. Observation of stochastic gravitational wave background from a cosmological phase transition would be a discovery of new physics beyond the standard model of particle physics, because the standard model predicts the electroweak and QCD phase transitions to be smooth crossover transitions. In this seminar I will describe in more technical detail than in the colloquia I give here how to calculate gravitational waves from first order cosmological phase transitions. I will describe in detail state-of-the-art methods for doing this, while pointing out common problems and traps that can lead to incorrect results. I will also show that there are substantial uncertainties even with state- of-the-art methods and comment on open questions and things which may be improved in the future.