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.

Timetable of department common room.

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 seminars at the Department of Theoretical Physics

Location: 3rd floor, 3.67, Bekesy 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.

• 17 February 2025, Karoly Seller (Eotvos) slides

  Primordial magnetic fields

  There is evidence today that galactic voids are permeated by a largely homogeneous and extremely weak magnetic field. While magnetic fields are not uncommon in the Universe, their presence in the low-density voids is somewhat perplexing. There are competing theories for the origin of these fields: they may be of galactic origins or entirely primordial. In this talk, we will begin by looking at how the combined magnetic field of galaxies is unlikely to explain the observed spectra. Then we turn to the alternative, primordial explanation, and after a short review of the relevant details (in particular of electroweak topological defects), we show how a primordial magnetic field spectrum may be generated through a simple lattice model and derive analytic properties. We end by commenting on the evolution of the primordial fields through the early Universe, and their expected form today.

• 24 February 2026, David Pesznyak (Eotvos) slides

  Is it worth to find Lefschetz thimbles?

  The fermionic sign problem severely limits Monte Carlo simulations of systems with complex actions. Contour-deformation methods in complexified field space (such as Lefschetz thimbles, holomorphic flow or sign optimization) offer systematic ways to reduce phase fluctuations, but their optimal use is still under active study. In this talk, I analyze a set of exactly solvable one-dimensional integrals arising as one-site limits of Hubbard-, Gross-Neveu-, Thirring-, and Chern-Simons-like models. These toy models allow for a detailed comparison of Lefschetz thimbles, finite-time holomorphic flow contours, and numerically optimized continuous contours. We find that the convergence toward thimble results under holomorphic flow is generically non-monotonic, with an optimal finite flow time where the sign problem is weaker than on the thimbles themselves. Moreover, numerically optimized contours consistently outperform both thimbles and flowed contours, indicating that greater flexibility in contour choice can substantially improve sign-problem mitigation. The talk is based on: Phys.Rev.D 113 (2026) 1, 014506.

• 3 March 2026, Lorenz von Smekal (Giessen)

  Quark numbers and percolation of electric center fluxes in QCD

  We construct a gauge-invariant measure for deconfinement based on the percolation of electric center fluxes in full lattice QCD, and predict an associated geometric phase transition without a thermodynamic singularity. Our percolation measure agrees with the Z_N center-symmetry transition in the pure SU(N) gauge theory. In the corresponding Z_N-spin models, this percolation phase transition persists into the crossover region with explicit symmetry breaking along the Kertesz line, and in fact reduces to pure bond percolation for asymptotically large external fields. We therefore also predict a percolation phase transition for QCD with physical quarks, and perhaps even in the chiral limit, thus always yielding a clear distinction between confined and deconfined phases. The gauge invariance of the spanning probability as the order parameter for this geometric phase transition ensures that physical states remain colorless at all temperatures and densities. We discuss the strong and weak-coupling limits, and explicitly illustrate the mechanism in the flux-tube model representation of the effective theory for QCD at strong coupling with heavy quarks.

• 10 March 2026, Attila Pasztor (Eotvos)

  TBA

• 17 March 2026, Yunxin Ye (University of Jena)

  Quantum Field Theory of relativistic Luttinger fermions

  TBA

• 24 March 2026, Tamas Kovacs (Eotvos)

  TBA

• 31 March 2026, Sandor Katz (Eotvos)

  TBA

• 14 April 2026, Timea Vitos (Eotvos, Uppsala University)

  TBA

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 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: