Summer semester 2026

Tuesday seminars start at 15:15. Friday seminars start at 14:15.

Unless otherwise stated, the seminars will be held in PHY 5.1.34A.

Fri, 24th Apr

  • Time: 14:15
  • Speaker: Yuto Sugimoto (Tohoku University)
  • Invited by: T. Wettig
  • Title: Tensor renormalization group method for (3+1) dimensional QCD in the strong coupling limit

Tue, 28th Apr

  • Time: 15:15
  • Seminar cancelled

Fri, 8th May

  • Time: 14:15
  • Speaker: Sasa Prelovsek (University of Ljubljana and the Jožef Stefan Institute)
  • Invited by: Sara Collins
  • Title: Structure and spectroscopy of exotic hadrons from lattice
Abstract I will review our recent lattice studies of exotic hadrons, in particular tetraquarks with two heavy quarks relevant to recent experimental discoveries. The states that reside above or slightly below threshold have been inferred from the scattering on the lattice. The structure has been extracted by probing the hadrons with the electromagnetic current, which renders the charge distributions of individual quark flavors, and enables distinction between molecular and diquark-antidiquark compositions.

Tue, 12th May

  • Time: 15:15
  • Speaker: Dr. Yang Fu (MIT)
  • Invited by: G. Bali
  • Title: Two-photon exchange contribution in hydrogen-like atoms from lattice QCD
Abstract The proton is one of the basic building blocks of all atoms. An accurate knowledge about the proton charge radius not only gives us useful information on the size and structure of the proton, but it also provides a crucial precision test of the Standard Model at low energy. In addition, it has an impact on the Rydberg constant, one of the most accurately measured physical constants. The most precise determination of the proton charge radius is from the measurement of the muonic hydrogen spectrum, while the theoretical uncertainty is dominated by a hadronic effect called two-photon exchange. In this talk, I will present the first lattice QCD calculation of the two-photon exchange contribution, as well as a result from combining dispersion relations and lattice QCD.

Tue, 26th May

No seminar (Day after Pentecost)

Fri, 5th Jun

  • Time: 14:15
  • Speaker: Amlan Chakraborty (U Milan)
  • Invited by: Taushif Ahmed
  • Title: Feynman integrals through finite basis and Frobenius expansion

Tue, 9th Jun

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Fri, 12th Jun

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Tue, 16th Jun

  • Time: 15:15
  • Speaker: Dr. Mir Mehedi Faruk
  • Invited by: Taushif Ahmed
  • Title: de Sitter Geometry: Geodesics, Blackholes and Correlators
Abstract This talk reviews recent progress on the geometry of black holes in de Sitter space. We describe the causal structure of these spacetimes and discuss its imprint on the (bulk) correlators

Fri, 19th Jun

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Tue, 23th Jun

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Fri, 26th Jun

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Tue, 30th Jun

  • Time: 15:15
  • Speaker: Prof. Christian Schubert (Universidad Michoacana de San Nicolas de Hidalgo Mexico)
  • Invited by: Taushif Ahmed
  • Title: String-theory methods in perturbative gauge theory and gravity
Abstract It has been understood since the eighties that string theory amplitudes are in various aspects better organised than amplitudes in ordinary quantum field theory. One can try to exploit this fact either by representing field theory amplitudes as the infinite string-tension limit of string amplitudes (``string-based formalism’’), or by representing them by worldline path integrals, and evaluating those in a way analogous to the Polyakov path integral in string theory (``string-inspired formalism’’). Here I review and compare both approaches, using examples from strong-field QED, QCD and gravity.

Fri, 3th Jul

  • Time: 14:15
  • Speaker: Professor Laurence Yaffe (University of Washington)
  • Invited by: G. Bali
  • Title: Resurrecting the coherent state variational algorithm for large N gauge theories
Abstract The feasibility of studying, numerically, properties of infinite volume QCD-like theories in the large N limit using coherent state variational methods is reassessed. An entirely new implementation of this approach is described, applicable to SU(N) lattice gauge theories, with or without fundamental representation fermions, on cubic lattices of up to four dimensions. In addition to various test cases, initial results are presented for Hamiltonian Yang-Mills theory on an infinite two-dimensional spatial lattice.

Tue, 7th Jul

  • Time: 15:15
  • Speaker: Raphael Lehner (KEK TSUKUBA)
  • Invited by: T. Wettig
  • Title: Determining Two-Pion Scattering Lengths in the O(4) Non-Linear Sigma Model
Abstract We investigate the determination of the s-wave scattering length in the O(4)-symmetric φ^4 theory in the symmetry-broken phase. The theory is simulated on a four-dimensional lattice in the strong-coupling limit with a small external symmetry-breaking field. This model provides a controlled setting for testing methods used to extract low-energy scattering observables from lattice simulations. We focus on the isospin-0 and isospin-2 two-pion channels and compare perturbation theory, the finite-volume formalism of Lüscher, and the Euclidean correlator approach of Maiani and Testa for the extraction of the scattering length.

Fri, 10th Jul

  • Time: 14:15
  • Speaker: Maren Käfferlein
  • Invited by: Simon Pfahler
  • Title: Investigating the analytic structure of machine-learning models for the Dirac equation
Abstract In lattice QCD, solving the Dirac equation requires the inversion of the Wilson--Dirac operator, which is computationally expensive. In the work 'The Analytic Structure of Machine-Learned Solvers and Preconditioners for the Dirac Equation', three different gauge-equivariant neural networks were constructed and trained as solvers and preconditioners. The analytic structure of these models was investigated by comparing the learned weights to established methods. The weights corresponding to the Jacobi iteration, the GMRES algorithm and the hopping expansion were analytically derived and subsequently compared to those of the trained networks. Furthermore, it was investigated whether and how weight deviations of the trained models affect their performance as solvers and preconditioners.

Tue, 14th Jul

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Fri, 17th Jul

No seminar (Tag der Physik und Mathematik, tbc)

Past Seminars