Lattice Gauge Theory group
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. Since 2011 we are a CUDA Research Center.
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 {at} bodri {dot} elte {dot} hu or Daniel Nogradi at nogradi {at} bodri {dot} elte {dot} hu.
Our activities are funded by the Lendulet grant of the Hungarian Academy of Sciences and by the OTKANF104034 grant of OTKA.
We are also grateful to our past funding agencies, the EU Framework Programme 7 grant (FP7/20072013)/ERC No 208740.
Research
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
Seminar
Weekly seminars of the Department of Theoretical Physics
Location: 2nd floor, 2.54, Novobatzky room
Time: Wednesdays at 14:15

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 Smatrix 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 lowenergy scattering of quasiparticles 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 manybody systems selfthermalize to a certain extent: their evolution from a nonequilibrium 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 nonequilibrium time evolution of the integrable spin1/2 anisotropic Heisenberg (XXZ) spin chain, and we found that various shortranged spin correlators in the longtime 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 longstanding 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 quarkantiquark pair free energies and the electric and magnetic screening masses in the QGP.

1 October 2014, Guido Franchetti (HeriotWatt 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 4dimensional Riemannian manifolds. In this talk I will review the original proposal as well as more recent work about ALF gravitational instantons as models for multiparticle 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 threecomponent 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 schemedependence in the FRG Method slides
The Functional Renormalization Group (FRG) method has been constructed to perform the renormalization nonperturbatively 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 WegnerHoughton and Polchinski equations by the appropriate choice of the so called regulator function, i.e. the renormalization scheme. FRG equations are integrodifferential 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 schemedependent too. I discuss this renormalization schemedependence 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 protonproton 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 nexttoleading order and today fully differential results at nexttonexttoleading 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 socalled 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 systemenvironment 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 nonperturbative 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)
BoseEinstein condensation and Silver Blaze in the 2loop Phiderivable approximation slides
We numerically study the chemical potentialtemperature phase diagram of the O(2) model within the 2loop truncation of the Phiderivable 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 HartreeFock approximation and with lattice simulations. We discuss the loss of solution strongly connected with the Goldstonetheorem.

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 4manifold 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 4manifold only hence possesses a diffeomorphism group symmetry. Motivated by the GelfandNaimarkSegal construction and the DouganMason construction of quasilocal energymomentum 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 3dimensional 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 4point coupling (with dimension mass) is small, the beta function associated to the running 4point 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 nonzero 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.
For students
Our group offers TDK, diploma and PhD topics in Lattice Field Theory.
Please contact Sandor: katz {at} bodri {dot} elte {dot} hu
or Daniel: nogradi {at} bodri {dot} elte {dot} hu
in case you are interested.
Current topics include:
 QCD thermodynamics
 SU(N) gauge theory with topological lattice action
 O(3) nonlinear sigma model with topological term
 Beyond Standard Model  technicolor
People
professor
2001 PhD  Eotvos University, Hungary
20012003 postdoc  DESY, Hamburg, Germany
20032005 postdoc  University of Wuppertal, Germany
20062012 assistant professor  Eotvos University, Hungary
2012 professor  Eotvos University, Hungary
katz {at} bodri {dot} elte {dot} hu
postdoc
2013 PhD  University of Calcutta, India
2013 postdoc  Eotvos University, Hungary
santanu {at} bodri {dot} elte {dot} hu
assistant professor
2005 PhD  University of Leiden, the Netherlands
20052007 postdoc  University of Wuppertal, Germany
20072009 postdoc  UCSD, USA
20092011 senior research fellow  Eotvos University, Budapest
2011 assistant professor  Eotvos University, Budapest
nogradi {at} bodri {dot} elte {dot} hu
PhD student
2010  Eotvos University, Hungary
apasztor {at} bodri {dot} elte {dot} hu
postdoc
2013 PhD  University of Pecs, Hungary
2013 postdoc  Eotvos University, Budapest
pittler {at} bodri {dot} elte {dot} hu
MSc student
2014  Eotvos University, Hungary
MSc student
2014  Eotvos University, Hungary
PhD student
2010  Eotvos University, Hungary
trombitas {at} ludens {dot} elte {dot} hu
BSc student
2014  Eotvos University, Hungary
Former members
2009 PhD  Eotvos University, Hungary
2010 postdoc  University of Regensburg, Germany
endrodi {at} general {dot} elte {dot} hu
1996 PhD  UCLA, USA
19961998 postdoc  University of Colorado, Boulder, USA
19982000 postdoc  University of Leiden, the Netherlands
20002002 postdoc  DESY, Zeuthen, Germany
20022011 professor  University of Pecs, Hungary
2011 senior researcher  ATOMKI, Debrecen, Hungary
kgt {at} fizika {dot} ttk {dot} pte {dot} hu
20052006 research assistant  University of Wuppertal, Germany
2007 assistant lecturer  University of Pecs, Hungary
2010 PhD  Eotvos University, Hungary
2010 postdoc  University of Wuppertal, Germany
tothbalint {at} szofi {dot} elte {dot} hu
Recent papers

Can the Higgs Impostor Hide Near the Conformal Window?.
By Zoltan Fodor, Kieran Holland, Julius Kuti, Daniel Nogradi, Christopher Schroeder, Chik Him Wong.
10.1142/9789814566254_0002.

Freezeout parameters from electric charge and baryon number fluctuations: is there consistency?.
By S. Borsanyi, Z. Fodor, S.D. Katz, S. Krieg, C. Ratti, K.K. Szabo.
[arXiv:1403.4576 [heplat]].

Freezeout parameters: lattice QCD meets heavyion experiments.
By Sz. Borsanyi, Z. Fodor, S.D. Katz, S. Krieg, C. Ratti, K. Szabo.
PoS QCDTNTIII (2014) 033.

The chiral condensate from the Dirac spectrum in BSM gauge theories.
By Zoltan Fodor, Kieran Holland, Julius Kuti, Daniel Nogradi, Chik Him Wong.
[arXiv:1402.6029 [heplat]].

Charmonium spectral functions from 2+1 flavour lattice QCD.
By Szabolcs Borsanyi, Stephan Durr, Zoltan Fodor, Christian Hoelbling, Sandor D. Katz, Stefan Krieg, Simon Mages, Daniel Nogradi et al..
[arXiv:1401.5940 [heplat]].
10.1007/JHEP04(2014)132.
JHEP 1404 (2014) 132.

Local CPviolation and electric charge separation by magnetic fields from lattice QCD.
By G.S. Bali, F. Bruckmann, G. Endrodi, Z. Fodor, S.D. Katz, A. Schafer.
[arXiv:1401.4141 [heplat]].
10.1007/JHEP04(2014)129.
JHEP 1404 (2014) 129.

Can a light Higgs impostor hide in composite gauge models?.
By Zoltan Fodor, Kieran Holland, Julius Kuti, Daniel Nogradi, Chik Him Wong.
[arXiv:1401.2176 [heplat]].

Full result for the QCD equation of state with 2+1 flavors.
By Szabocls Borsanyi, Zoltan Fodor, Christian Hoelbling, Sandor D. Katz, Stefan Krieg, Kalman K. Szabo.
[arXiv:1309.5258 [heplat]].
10.1016/j.physletb.2014.01.007.
Phys.Lett. B730 (2014) 99104.
Computing
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 primary resource is a 128 node cluster with two NVIDIA GTX 275 cards in each node, hosted in Budapest. There is also a 60 node cluster with one NVIDIA GTX 8800 card per node.
In addition we also have access to the Juropa cluster and the BlueGene/P installation in Forschungszentrum Juelich, Germany.
Our collaboriation with the University of Wuppertal, Germany also allows us to use several PC and GPU clusters there.
In case you are interested you can see a map of GPU cluster installations throughout the world dedicated to Lattice Gauge Theory.
For visitors
You will most likely stay at the Peregrinus hotel in the downtown area of Pest.
The simplest way to get to/from your hotel from/to the airport is by taxi. Ask for the fixed rate which should be around 2022 euros.
Our department is on the Buda side of the Danube very close to the Petofi Bridge and it is about a 3035 minutes walk from the hotel:
You exit your hotel, walk past the Great Market Hall (definitely worth a closer look if you have about half an hour or an hour!) and the Corvinus University, cross the Danube on the Szabadsag Bridge and walk South. You will pass the Budapest University of Technology and the Petofi Bridge and our building will be a redish sevenstory building on the right. The Department of Theoretical Physics is on the first floor on the Danube facing side of the building: