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.
Timetable of department common room.
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.

24 September 2024, Timo Karkkainen (Tallinn) slides
Neutrino phenomenology from uncertainty principle?
Generalized uncertainty principles are effective changes to the Heisenberg uncertainty principle that emerge in several quantum gravity models. We study the consequences of two classes of these modifications on neutrino phenomenology: oscillation probabilities, coherence lengths and nonstandard neutrino interactions. We find the constraints imposed by oscillation experiments and in particular the IceCube neutrino observatory to be as strict as the current bounds.

1 October 2024, Sandor Varro (ELI, ERIC, ALPS, Szeged) slides
Mass formula for the X17 particle and the proton size
The recent observations of anomalous angular correlations of electronpositron pairs, stemming from the products of several nuclear reactions, have been interpreted by assuming the existence of a neutral boson of rest mass of about 17 MeV/c^2, called the X17 particle. The discovery of this socalled "ATOMKI anomaly" has initiated several theoretical studies, however still there is no agreement on the very nature of this hypothetical particle. In the present talk we rely on quantum electrodynamics, in order to show a possible derivation of the abovementioned mass. We use the exact solutions of the Dirac equation of the system of a charged particle and quantized electromagnetic plane waves, which we apply to a proton. These nonperturbative solutions contain a frequency upshift of the radiation quanta, which results in the appearance of an effective electromagnetic mass, so we encounter with a sort of massive photons. The derived formula for the invariant mass, besides a firstpriciple statistical factor, contains only the Sommerfeld fine structure constant and the proton mass, and yields the numerical value 17.0087 MeV/c^2, in a good agreement with the experimental data. In our formalism the mass of the X17 particle and the proton size are connected, and we have also derived the numerical value 0.846299 fm for the proton radius, which is quite close to the measured "smaller proton charge radius". In the talk we shall outline this reasoning on the proton size, and also discuss the recent "proton size puzzle", whose solution still represents a challenge in quantum electrodynamics.

8 October 2024, Balazs Pozsgay (Eotvos)
Free fermions in disguise
Recently a new family of lattice spin1/2 models was discovered, which have a hidden free fermionic solution. Most of these models exist in 1D (they are spin chain models), but some of them live in higher dimensions. The key property of the models is that the total Hamiltonian can be expressed as a bilinear function in the hidden fermions, but the Hamiltonian density is not a simple function of the fermions. We review these models, by focusing on the original model of Paul Fendley, discovered in 2019. We also discuss the contributions of our research group: they include the computation of real time correlation functions of boundary operators.

15 October 2024, Levente Pristyak (Eotvos) slides
Dynamics of OneDimensional Integrable Systems
Integrable quantum models are special manybody systems with a large number of conserved quantities that significantly constrain their dynamics. As a result, these systems display unique equilibration properties, governed by the Generalized Gibbs Ensemble (GGE) and Generalized Hydrodynamics (GHD). In this talk, we explore several interconnected topics, all tied to the broader theme of equilibration in integrable systems. In the first part of the presentation, we investigate the current operators of the XXZ and XYZ spin1/2 chains and derive an exact formula for their mean values, which serves as a theoretical foundation for GHD. The second part of the talk focuses on "simple" integrable systems, that have notably simple scattering phases, while still being genuinely interacting. We study the dynamics of these models and explore another form of thermalization breakdown in the form of Hilbertspace fragmentation.

22 October 2024, Istvan Vona (Eotvos) slides
Exact real time dynamics with free fermions in disguise
Continuing on the talk "Free fermions in disguise" from two weeks ago, we will revisit the construction of the hidden fermions in detail. We will discuss how to measure the model's correlators on a quantum computer and obtain exact results for certain special correlators (even in the thermodynamical limit). Their importance for quantum computing will be clarified, and we will also see what is (not) feasible with current hardware.

5 November 2024, David Pesznyak (Eotvos) slides
Gauge field digitization in the Hamiltonian limit
The use of quantum computers could circumvent the complex action problem hampering firstprinciples studies of gauge theories in real time or at finite density. One of the main bottlenecks of quantum computers is the limited number of available qubits. One approach to mitigate this bottleneck is the discretization of continuous gauge groups to their discrete subgroups, which introduces systematic uncertainties. Previously, discrete subgroups and dense subsets of gauge groups had been investigated with lattice field theory simulations on classical computers but not yet in the Hamiltonian limit, where the temporal lattice spacing approaches zero while the spatial lattice spacing is kept fixed. In this work, we take the first steps in studying the systematics associated with digitization by performing anisotropic Euclidean simulations and taking the Hamiltonian limit.

12 November 2024, Gabriella Pasztor (Eotvos)
Precise determination of the W mass with the CMS detector
The value of the W boson mass, determined with a 6 MeV uncertainty from global standard model fits and measured by several experiments at LEP, Tevatron and LHC, has attracted a lot of attention in the last two years. The CMS experiment has performed the most precise measurement to date at the LHC using protonproton collision data corresponding to an integrated luminosity of 16.8 / fb recorded in 2016. The W boson mass is obtained using a novel method from a fit of the twodimensional transverse momentum  pseudorapidity distribution in a large sample of W > (mu,nu) decays, categorized by charge. I will give an overview of the applied technique and discuss the results that for the first time broke the 10 MeV precision level at the LHC.

19 November 2024, Sam van Thurenhout (Wigner)
AllN structure of leadingtwist alien operators in QCD
Parton evolution equations in QCD are controlled by the anomalous dimensions of leadingtwist gaugeinvariant spinN operators. Under renormalization, these mix with gaugevariant operators of the same quantum numbers, referred to as alien operators. In this talk we address the systematic study of these alien operators at arbitrary spin N . In particular, using generalized BRST symmetry relations, we derive their couplings and Feynman rules at all values of N . We observe how the allN structure of the generalized BRST constraints relates the couplings of alien operators with n+1 gluons to those with n gluons. Realizing a bootstrap, we present all oneloop results necessary for performing the operator renormalization up to four loops in QCD.

26 November 2024, Oliver Schnetz (Universitat Hamburg)
Graphical functions
I give an introduction into the theory of graphical functions which is a tool to perform high loop order calculations in massless quantum field theories. Currently the theory of graphical functions is upgraded to gauge theories (originally only spin zero was covered). I will also give a short account on the status of the upgrade.

3 December 2024, Karoly Seller (Eotvos)
TBA

10 December 2024, Andras Laszlo (Wigner)
On the running and the UV limit of Wilsonian renormalization group flows
In this talk we describe a recent result [Class.Quant.Grav.41(2024)125009] which states that, under mild conditions, a Wilsonian renormalization group (RG) flow of Feynman correlators, which extends to arbitrary regularization strengths, has a factorization property. Namely, there exists a regularizationindependent distributional Feynman correlator (UV limit), from which the flow originates via an algebric ansatz. In addition, we will mention a newer development, stating the analogy of the above theorem in the context of Euclidean Feynman measures. Namely, under mild conditions, a Wilsonian RG flow of Feynman measures extending to arbitrary regularization strenghts has a factorization property: there exists some ultimate Feynman measure (UV limit) on the distributional fields, such that the regularized instances in the flow are obtained from this UV limit via taking the marginal measure against the regulator. Some theorems about the flow and UV limit of the corresponding action functional can also be stated.
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
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
postdoc
2020 PhD  University of Debrecen, Hungary
2020  postdoc  Eotvos University, Hungary
PhD student
2021 Eotvos University, Hungary
PhD student
2021 Eotvos University, Hungary
Former members
PhD student
2023 postdoc, Technical University, Hungary
20182023 Eotvos University, Hungary
PhD student
2016  2023 Eotvos University, Hungary
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: