DEPARTMENT OF PHYSICS / HIP JOINT COLLOQUIA / SEMINARS 2026

  • Tuesday 20 January 2026 at 10:15 in A315 and using Zoom: Michal Heller (Ghent)
    New look at self-similar dynamics far from equilibrium
    Abstract:     Equilibrium systems are simple in the sense that they are characterized by only a few macroscopic parameters, such as temperature or chemical potential. Far-from-equilibrium dynamics, by contrast, appears overwhelmingly complex. Any emergent universality in this regime is therefore both rare and valuable, and calls for a deeper theoretical understanding. In this talk I will discuss a paradigmatic instance of such a universality: self-similar dynamics in time, where far-from-equilibrium evolution reduces to simple rescalings governed by a small set of scaling exponents and time-independent correlation profiles. These nonthermal fixed points play an important role across the energy scale: from theory of ultrarelativistic nuclear collisions to tabletop experiments with cold atomic gases. Drawing analogies with black-hole physics and holography, I will explain what controls the attractive nature of nonthermal fixed points and why vastly different microscopic systems can flow toward the same universal behavior. Pushing these analogies further, I will show that nonthermal fixed points give rise to a novel form of fluid mechanics that is intrinsically far from equilibrium. This opens the door to systematic comparisons between familiar near-equilibrium liquids and this newly identified far-from-equilibrium fluid, some aspects of which I will address. Based on 2502.01622 with Lescluze, 2504.18754 with Berges, Denicol and Preis and 2510.15016 with Lescuze, Mazeliauskas, Scheihing-Hitschfeld and Werthmann.
    Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=fd0d9726-ef23-446c-9dc8-c4675df485c2
  • Thursday 22 January 2026 at 10:15 in A315 and using Zoom : René Meyer (Würzburg)
    Aspects of PT symmetric Non-Hermiticity in AdS/CFT and in SYK models
    Abstract:     Investigations of non-hermitian quantum systems recently has drawn much interest in the field of holography and the AdS/CFT correspondence. In this talk, I will focus on non-hermiticity of the PT symmetric type and, after a short introduction into the subject, present several results for PT symmetric systems of interest in holography: In the first part of the talk, I will discuss our recent [1] investigation of the phase structure and the interaction induced quantum critical conductivity in a PT symmetric non-hermitian holographic metal. In particular the conductivity shows interesting new features in the different phases, which are qualitatively reproduced in a PT symmetrically deformed version of Landau-Ginzburg theory. In the second part of the talk, I will present analytic and numerical work [2] on the operator size growth in Lindbladian SYK models. I will in particular present a new timescale, the plateau time, after which the operator size growth reaches a plateau. Finally, I will present recent work [3] on the entanglement structure in these Lindbladian SYK models, and a new entanglement measure with better properties for non-hermitian systems.
    [1] Z.Y. Xian, D. Rodriguez-Fernandez, Z.H. Chen, Y. Liu, R. Meyer, SciPost Physics 16 (2024)
    [2] J.S. Liu, R. Meyer, Z.Y. Xian, JHEP 08 (2024)
    [3] Z.H. Chen, R. Meyer, Z.Y. Xian, arXiv:2508.09261
    Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=009b011c-6668-458b-acf4-2eb25e2f8eea
  • Tuesday 24 February 2026 at 10:15 in A315 and using Zoom: Viljami Leino (Odense)
    Strong coupling constant from the static energy
    Abstract:     The static energy between the static quark and the static antiquark is a well studied observable on the lattice. For short distances, the static energy can be calculated both on the lattice with the use of Wilson line correlators, and with the perturbation theory up to three loop accuracy with leading ultrasoft log resummation. Comparing the perturbative expression and lattice data allows for precise measurement of the strong coupling constant of QCD. I will show static energy measurements from lattice simulations with a different number of dynamical fermion flavors and present the current status of extracting the strong coupling constant from this data.
    Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=1beecd5f-6291-4408-8b70-385c0adafc42