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.

8 February 2017, Arpad Lukacs (Wigner)
Stabilisation of semilocal strings by dark scalar condensates slides
Semilocal and electroweak strings are wellknown 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 Higgsportaltype 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 nonintegrable 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 nonequilibrium 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 lowlying particle excitations even for moderate size quenches. In the ferromagnetic phase these particles are the various nonperturbative 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 (MTADE Particle Physics Research Group, Debrecen)
Offshell 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 toppair 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 stateoftheart description of the process. Given the extremely short lifetime of the top quark, any realistic simulation of tt+jets cannot prescind from a genuine multiparticle calculation, which puts serious challenges when going beyond the leading order in perturbation theory. For this reason theoretical predictions are often restricted to onshell top quarks, and decays are treated in the Narrow Width Approximation under the assumption that the offshell 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 offshell effects is phenomenologically relevant. Then, motivated by these arguments, I will show recent progress in the calculation of complete offshell 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 nontopological. 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, nontopological 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 twoparticle irreducible (2PI) formalism along with other methods involving a selfconsistent 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 twoloop 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 (MTAWigner)
Self trapped gravitational waves (geons) with antide 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 antide Sitter (AdS) metric. AdS geons are timeperiodic regular localized vacuum solutions without any radiation loss at infinity. A perturbative construction in terms of an amplitude parameter shows that there are oneparameter families of AdS geon solutions emerging from combinations of samefrequency 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)
PseudoGoldstone excitations in chiral Yukawatheories 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 Yukawainteraction, 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 pseudoGoldstone 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 nonperturbative Functional Renormalisation Group technique.

19 April 2017, Peter Vecsernyes (WignerMTA)
A toy model of selective measurement in quantum mechanics slides
The nonselective and selective measurements of a selfadjoint 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 nonunitarity of time evolution arises as an effective description of the interaction with the measuring apparatus. The dynamics we present is a twostep dynamics: the first step is the nonselective 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 nonlinear 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 lowmass 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 Mdwarf 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.
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: