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 an NVIDIA GPU 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
See the archive for seminars in past years.

10 February 2016, Diego Correa (La Plata, Argentina)
1loop exponentiation for large rank Wilson loops slides
In this talk I will describe Wilson loops in N=4 super YangMills, for external particles in krank 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 1loop result. This will be verified for a generic family of Wilson loops in the strong coupling limit performing a classical Dbrane 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 BetheYang 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 MTAELTE)
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, 5dimensional effective interactions are postulated. SU(2)xU(1) gauge invariance implies additional dim5 interactions with the weak bosons leading to nontrivial constraints on the validity of the effective theory. The effective interactions can be generated at 1loop by additional coloured and charged vectorlike quarks, these favour narrowwidth 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 NambuJonaLasinio model of Quantum Chromodynamics (QCD2) both at zero and finite matter density using nonperturbative techniques (nonAbelian bosonization and Truncated Conformal Space Approach). At zero density we describe a formation of fermion threequark (nucleons and Deltabaryons) and boson (twoquark mesons, sixquark 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 quasilongrange (QLR) order and also a phase of a baryon TomonagaLuttinger liquid (strange metal). The QLR order results as a condensation of scalar mesons (the density wave) or sixquark 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 LeeYang 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 (MTAELTE)
Search for a New Heavy Boson in the diphoton 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 diphoton final state in the 2015 LHC data collected at a centreofmass 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 diphoton search as well as the newly emerging results from other final states such a new particle could decay into.

30 March 2016, Gyula Bencedi (MTAWigner)
Multiplicity dependence of charged pion, kaon, and (anti)proton production at large transverse momentum in pPb collisions at 5.02 ATeV
The discovery of fluidlike 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 flowlike effects and new hadronization mechanisms like recombination and jet quenching. In this talk I am going to present the recent results, arXiv:1601.03658v1 [nuclex], on the multiplicity dependence of charged pion, kaon and (anti)proton production in pPb 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, pPb and PbPb collisions will be shown, in addition the nuclear modification factor for identified particles in nonsingle diffractive pPb collisions will be discussed as well.

6 April 2016, Janos Balog (MTAWigner)
Masscoupling relation in quantum integrable models slides
We determine exactly the masscoupling relation in the simplest multiscale quantum integrable model, the homogenous sineGordon 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 masscoupling 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 KantowskiSachs cosmologies slides
A general treatment of vorticityfree, perfect fluid perturbations of KantowskiSachs 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 gravitomagnetic, 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 gravitomagnetic 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 KantowskiSachs 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 QuarkGluon Plasma (QGP), and present the current stateoftheart 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 Yukawamodel. We determine the phase diagram on the coupling constant space, and discuss the role of the different approximation schemes (mean field, oneloop, FRG LPA). Finally I will mention some possible applications.

18 May 2016, Szilveszter Harangozo (MTAWigner)
A new HeavyIon 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)
Highenergetic 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 highenergy 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 sarkanykonfiguracio  egy megoldas csodai slides
A centralis konfiguraciok nagy szerepet jatszanak az ntest 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 haromtestproblema centralis konfiguracioi az EulerLangrangemegoldasok. n>3ra egyenlo tomegu szimmetrikus elrendezesek ismertek. Az eloadas roviden attekinti az eddigi legfontosabb eredmenyeket, es bemutat egy kozelmultban kapott analitikus megoldast a negytestproblema egy tengelyszimmetrikus esetere.

22 June 2016, Attila Krasznahorkay (ATOMKI)
On the track of the dark forces slides
Electronpositron 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 lunchtable 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.
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
postdoc
2009 PhD  University of Pisa, Italy
20102010 postdoc  IPhT/CEASaclay, France
20102012 postdoc  University of Zaragoza, Spain
20122015 postdoc  ATOMKI, Debrecen, Hungary
giordano {at} bodri {dot} elte {dot} hu
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
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
BSc and MSc 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
PhD student
2010  Eotvos University, Hungary
apasztor {at} bodri {dot} elte {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. The fare should be around 30 euros. Uber also works in Budapest :)
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: