We are the lattice gauge theory group at the Eotvos University in Budapest, part of the Department of Theoretical Physics at the Faculty of Science.

Currently there are nine members and we are seeking new ones. Positions are available for PhD students and postdocs for 2 - 4 years appointments. If you are interested please email Sandor Katz at katz@bodri.elte.hu or Daniel Nogradi at nogradi@bodri.elte.hu.

Our activities are and were funded by various funding agencies for which we are grateful, these include the Lendulet grant of the Hungarian Academy of Sciences, the OTKA-NF-104034 grant of OTKA and the EU Framework Programme 7 grant (FP7/2007-2013)/ERC No 208740.

Our primary interests are:

• Chiral symmetry restoration and deconfinement in QCD with Wilson fermions
• Finite chemical potential
• QCD hadron spectrum
• Eigenvalue distributions of the overlap Dirac operator
• Strongly interacting Higgs sector - strong dynamics
• Conformal gauge theories

Weekly ELFT seminars at the Department of Theoretical Physics

Location: 2nd floor, 2.54, Novobatzky room, 1117 Budapest, Pazmany Peter setany 1/a

If you'd like to receive seminar email announcements please write to nogradi@bodri.elte.hu

Time: Tuesdays at 14:15

See the archive for seminars since 2014.

• 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)

Our group offers BSc/MSc diploma, PhD and TDK topics in Lattice Field Theory.

Please contact Sandor: katz@bodri.elte.hu or Daniel: nogradi@bodri.elte.hu in case you are interested.

Current topics include:

• QCD thermodynamics
• 2 and 4 dimensional CFT
• Beyond Standard Model

Since it is tricky to locate all papers by a large number of people whose names are not unique on inspire, you can try various search queries:

• Papers by Sandor Katz and Zoltan Fodor
• Papers by Sandor Katz and Gergely Endrodi
• Papers by Sandor Katz and Matteo Giordano
• Papers by Tamas Kovacs
• Papers by Daniel Nogradi

Our group has access to a number of high performance computer installations in Europe and also maintains several PC and GPU clusters on site in Budapest.

Our department is on the Buda side of the Danube very close to the Petofi Bridge:

The Department of Theoretical Physics is on the sixth floor opposite the Danube facing side of the building: