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