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.
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 OTKANF104034 grant of OTKA and 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 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.

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 heavyion 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 PbPb 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 fourmanifolds
Making use of its smooth structure only, out of a connected oriented smooth 4manifold 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 4manifold 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 4manifold this universal von Neumann algebra admits a particular representation on a Hilbert space such that its unitary equivalence class is preserved by orientationpreserving diffeomorphisms consequently the Murrayvon Neumann coupling constant of this representation is welldefined and gives rise to a new and computable realvalued smooth 4manifold 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 4manifold 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 PressSchechter 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 spinrelated observables at NLO electroweak precision are presented: Z+jet, W+jet (also including NNLO QCD) and topantitop pair production. In addition, the first steps towards a more efficient approach to handle highmultiplicity jet processes is presented, via the nexttoleading 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 nonperturbative 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 finitedimensional 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 laboratoryscale experimental setups. 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 dynamicsmotivated problems focusing on the transitions between different states of "minimal models" of the midlatitude 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 illdefined. The Feynman integral formulation has, however, a differential reformulation: the master DysonSchwinger (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 Hamiltonianagnostic 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.
For students
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
People
assistant professor
2009 PhD  University of Pisa, Italy
20102010 postdoc  IPhT/CEASaclay, France
20102012 postdoc  University of Zaragoza, Spain
20122015 postdoc  ATOMKI, Debrecen, Hungary
20152018 postdoc  Eotvos University, Budapest, Hungary
PhD student
2018 Eotvos University, Hungary
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
professor
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
2020 professor, Eotvos University, Hungary
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
2012  2020 assistant professor  Eotvos University, Budapest
2020 professor  Eotvos University, Budapest
postdoc
2015 PhD  Eotvos University, Hungary
20162018 postdoc  Wuppertal University, Germany
2018 postdoc  Eotvos University, Hungary
PhD student
2016 Eotvos University, Hungary
postdoc
2020 PhD  University of Debrecen, Hungary
2020  postdoc  Eotvos University, Hungary
Former members
2009 PhD  Eotvos University, Hungary
20102015 postdoc  University of Regensburg, Germany
2016 Emmy Noether group leader  University of Frankfurt, Germany
2020 professor  University of Bielefeld, Germany
2013 PhD  University of Calcutta, India
20132016 postdoc  Eotvos University, Hungary
20162018 postdoc  National Chiao Tung University, Taiwan
2018 postdoc  Los Alamos National Laboratory, USA
2013 PhD  University of Pecs, Hungary
20132016 postdoc  Eotvos University, Budapest
2017 postdoc  Bonn University, Germany
2017 PhD  Eotvos University, Hungary
2017 postdoc  Wuppertal University, Germany
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
PhD student
2015 PhD  Eotvos University, Hungary
PhD student
2018 Eotvos University, Hungary
Publications
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.
For visitors
Our department is on the Buda side of the Danube very close to the Petofi Bridge, the address is Budapest 1117, Pazmany Peter setany 1/A:
The Department of Theoretical Physics is on the sixth floor opposite the Danube facing side of the building: