Ws2024

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.

Tue, 15th Oct

Fri, 18th Oct

  • Time: 14:15
  • Speaker: Marcel Rodekamp (University of Regensburg)
  • Invited by: S. Collins
  • Title: First Principle Calculations of the Hubbard model in the Presence of a Sign Problem.
Abstract In this talk we investigate a method for first principle calculations of the Hubbard model, inspired by the lattice QCD methods. The Hubbard model, and its extensions, is a well established and popular model for systems of strongly correlated electrons. Such systems have a special standing at the frontier of material science/condensed matter physics due to their rich and versatile properties. Many challenges can be shared between the models, in particular, when simulated in a grand canonical set up. I will focus on the application of Hybrid Monte Carlo for generating ensembles at a fixed set of model parameters in the presence of a fermionic sign problem. Further, I will discuss a variational basis of correlation functions which allows the extraction of particle excitation energies. All these topics are closely related to methods developed in lattice QCD, showing how different communities can benefit from each others expertise.

Tue, 22nd Oct

Fri, 25th Oct

  • Time: 14:15
  • Speaker: Thomas Ratzke (Master Vortrag)
  • Invited by: Tilo Wettig
  • Title: Neural Network Preconditioning for the Dirac Equation

Tue, 29th Oct

Fri, 1st Nov

All Saints' Day

Tue, 5th Nov

Fri, 8th Nov

Tue, 12th Nov

  • Time: 15:15
  • Speaker: Prof. V. Ravindran (IMSc, Chennai)
  • Invited by: T. Ahmed
  • Title: Going beyond NNLO QCD corrections to SIDIS

Fri, 15th Nov

Tue, 19th Nov

  • Time: 15:15
  • Speaker: Jeremy Green (DESY Zeuthen)
  • Invited by: S. Collins
  • Title: Baryon-baryon scattering in SU(3)-flavour-symmetric QCD
Abstract Understanding (hyper)nuclear physics from ab initio QCD has been a long-standing goal. By calculating finite-volume spectra on the lattice and using finite-volume quantization conditions, it is possible to determine baryon-baryon scattering phase shifts and bound states. I will discuss the challenges in these calculations, presenting results in the continuum limit at an SU(3) flavour-symmetric point, for the H dibaryon and the deuteron. As a spin-one state, the latter is complicated by the mixing of S and D waves, which we are able to resolve.

Fri, 22nd Nov

  • Time: 14:15
  • Speaker: Akaki Rusetsky (HISKP, Universität Bonn)
  • Invited by: G. Bali
  • Title: Finite-volume effects in the chiral limit
Abstract Some physical systems, which are studied on the lattice, in the broken symmetry phase feature massless or nearly massless excitations in the spectrum. Effective chiral Lagrangians can still be used to study the finite-volume effects in such systems. However, for the masses much smaller than the inverse size of the cubic box, the perturbative expansion should be organized differently from the standard regime (in which both these quantities are of the same order). At very low (zero) temperatures this goes under the name of the $\delta$-regime, where the so-called slow mode of the Goldstone boson field is singled out and treated non-perturbatively. In this talk we discuss the construction of a systematic perturbative expansion for the finite-volume energy spectrum of the non-linear $O(N)$ $\sigma$-model in the $\delta$-regime and show that the violation of the power-counting rules that emerges after the separation of the fast and slow modes can be dealt with to all orders by use of the threshold expansion. The known result for the rest-frame energy spectrum up-to-and-including next-to-next-to-leading order will be reproduced. Applications of the method to lattice QCD and the lattice models in condensed state physics will be discussed.

Tue, 26th Nov

  • Time: 15:15
  • Speaker: Archana Radhakrishnan (TIFR)
  • Invited by: G. Bali
  • Title: Exotic $T_{bc}$ Tetraquarks from Lattice QCD
Abstract Research into doubly heavy tetraquarks has become highly relevant, especially with the recent discovery of the doubly charmed tetraquark. In this talk, we present a lattice investigation of S-wave $D\bar{B}^{(*)}$ scattering within the isoscalar axial-vector and scalar channels. Both processes feature the flavor combination $bc\bar{u}\bar{d}$, which could potentially host tetraquarks.
Our calculations were conducted on four different $N_f= 2+1+1$ MILC gauge ensembles, with varying lattice spacings and volumes. Utilizing the amplitude analysis method by Lüscher, we extracted the scattering amplitudes from the finite-volume spectra. We examine the light quark mass ($m_{u/d}$) dependence of these amplitudes and extrapolate the amplitudes to the continuum. Our findings provide evidence for a bound state of the $bc\bar{u}\bar{d}$ tetraquark at the physical light quark mass point within both the scalar and the axial-vector channels.

Fri, 29th Nov

  • Time: 14:15
  • Speaker: Martin Hoferichter (University of Bern)
  • Invited by: S. Collins
  • Title: Excited states in nucleon correlation functions from chiral perturbation theory
Abstract Excited-state contamination is an important systematic effect in the calculation of nucleon matrix elements from lattice QCD. For sufficiently small pion masses and sufficiently large temporal separations, the expected size of the effects can be estimated from chiral perturbation theory, by collecting pole residues in the Euclidean. To assess the convergence of the expansion, especially in view of possible enhancements from Delta intermediate states, it is essential to study subleading terms in the expansion. I will present recent work in this direction, with applications to the axial charge of the nucleon and the pion-nucleon sigma term.

Tue, 3rd Dec

Wed, 4th December

  • !!!extra date!!!

  • Workshop Graduate School PP-HPC

Schedule: 10:00 Jonas Landgraf: Artificial discovery of scattering networks
11:00 FUTUR: Wege zur Unternehmensgründung

12:00 Lunch Break

13:30 Matt Pawelcyk: Amazon Web Services: Introduction to the cloud
14:30 Giovanni Pederiva: Demystifying quantum computing in lattice field theories

15:30 Coffee break
16:00 Lorenzo Barca: Multilevel sampling for glueball calculations and more
  • The talks will take place in PHY 5.1.34A.

Please register (with fullname and affiliation) here (external link), if you plan to participate.

Fri, 6th Dec

Tue, 10th Dec

  • Time: 15:15
  • Speaker: Julian Parrino (University of Regensburg)
  • Invited by: C. Lehner
  • Title: Coordinate-Space Calculation of the UV-Finite Electromagnetic Corrections to the Hadronic Vacuum Polarization Contribution to the Muon (g-2)
Abstract In the anomalous magnetic moment of the muon, the determination of the hadronic vacuum polarization (HVP) contribution must reach sub-percent precision in order for the Standard Model prediction to match the precision of the experimental measurement. To achieve this, one needs to include QED corrections that break the isospin symmetry, which is usually imposed in lattice calculations. One typically treats these corrections perturbatively in the electromagnetic fine-structure constant $\alpha$, expressing them through Feynman diagrams with hadronic n-point functions calculated in isospin symmetric QCD, where individual vertices are connected by the photon propagator.
We present a lattice QCD study of one of the disconnected diagrams, which is UV-finite and not suppressed by SU(3) flavour symmetry. The calculation is performed in a coordinate-space framework using the photon propagator in the continuum and infinite volume. Additionally we investigate a phenomenological model including the effects of the charged and neutral pion, as well as the eta- and eta'-meson, in order to guide the lattice QCD calculation.

Fri, 13th Dec

talk "Hadronic resonances from lattice QCD" by Fernando Romero-López (University of Bern) has been postponed to 17th of January 2025

Tue, 17th Dec

  • Time: 15:15
  • Speaker: Andreas Völklein (Master Vortrag)
  • Invited by: C. Lehner
  • Title: Importance sampling of coordinates in correlation functions with Markov chains

Fri, 20th Dec

talk "Bulk Statistics in Complex Spectra for Non-Hermitian Systems" by Dr. Mario Kieburg (University of Melbourne) has been cancelled

Winter break: 23rd Dec 2024 - 6th Jan 2025

Happy Holidays and New Year 2025!!!

Tue, 7th Jan

Fri, 10th Jan

Tue, 14th Jan

  • Time: 15:15
  • Speaker: Lukas Niggl (Master Vortrag)
  • Invited by: C. Lehner
  • Title: The octahedral group and automatic operator generation

Fri, 17th Jan

  • Time: 14:15
  • Speaker: Fernando Romero-López (University of Bern)
  • Invited by: G. Bali
  • Title: Hadronic resonances from lattice QCD
Abstract The majority of known hadrons in the low-energy QCD spectrum are resonances observed in multi-particle scattering processes. First-principles determinations of the properties of these unstable hadrons are a crucial goal in lattice QCD calculations. Significant progress has been made in developing, implementing and applying theoretical tools that connect finite-volume lattice QCD quantities to scattering amplitudes, enabling determination of masses and widths of various hadronic resonances. In this talk, I will discuss recent advances in lattice QCD studies of meson-baryon resonances, including the Delta(1232) and Lambda(1405) resonances, as well as three-hadron resonances such as the doubly-charmed tetraquark.

Tue, 21st Jan

  • Time: 15:15
  • Speaker: Andreas Hackl (Ph.D. student, University of Regensburg)
  • Invited by: C. Lehner
  • Title: Spectral analysis for nucleon-pion and nucleon-pion-pion states in both parity sectors using distillation with domain wall fermions

Fri, 24th Jan

Tue, 28th Jan

  • Time: 15:15
  • Speaker: Haoyu Wang (Master Vortrag)
  • Invited by: C. Lehner
  • Title: Finite Volume Corrections for HVP using ChPT, HP method and Lüscher Formalism

Fri, 31st Jan

talk by L. Ernstberger rescheduled to Feb, 14th

Tue, 4th Feb

  • Time: 15:15
  • Speaker: Ferdinand Tölkes (Master Vortrag)
  • Invited by: A. Schäfer
  • Title: Subtyping Whole Slide Images of Lymphoma with Deep Learning Methods

Fri, 7th Feb

Tag der Mathematik und Physik (14:00/H36)

Tue, 11th Feb

!!!extra seminar!!!

  • Time: 15:15
  • Speaker: Valentin Hausladen (Bachelor Vortrag)
  • Invited by: T. Wettig
  • Title: Preconditioning the Dirac equation for Wilson-clover fermions using gauge-equivariant deep neural networks

Fri, 14th Feb

!!!extra seminar!!!

  • Time: 14:15
  • Speaker: Leon Ernstberger (Master Vortrag)
  • Invited by: T. Wettig
  • Title: Approaches to dimensional reduction in cancer progression model calculations