René Meyer (Institute for Theoretical Physics and Astrophysics, University of Würzburg, Germany)
Aspects of PT symmetric Non-Hermiticity in AdS/CFT and in SYK models
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.
Cosmo: Wednesday, 11/02/2026, 11:30, Lecture Hall
Jorge Baeza-Ballesteros (DESY, Zeuthen, Germany)
Particle and gravitational wave emission from cosmic string loops
Cosmic strings are one-dimensional topological defects predicted to form in the early universe after a phase transition by a variety of extensions of the Standard Model, ranging from axion models to grand-unified theories. After forming, strings are expected to decay via the emission of both particles and gravitational waves (GWs), leading to the formation of a GW background (GWB) that may be detected by ongoing or future GW experiments. Traditionally, predictions of the GWB produced by cosmic strings are based on the Nambu-Goto (NG) approximation, in which the internal structure of the strings and their decay into particles are neglected. However, a correct interpretation of a positive GW signal would require of accurate predictions beyond the NG approximation that fully account for the field-theoretic nature of cosmic strings. In this talk I describe how the dynamics of cosmic strings can be simulated using field-theory lattice simulations, and how we have used such simulations to characterize the emission of particles and GWs from closed cosmic strings, called loops. Our results show that, contrary to NG expectations, cosmic string loops with lengths up to 10^5 times their core width decay predominantly via particle emission, with negligible poduction of GWs, with no indication that this behaviour may change for longer strings. We expect thee results will lead to a significant reduction of current predictions for the amplitude of the GWB produced by cosmic-string networks.
Cosmo: Wednesday, 18/02/2026, 11:30, Lecture Hall
Manuel Del Piano (University of Southern Denmark, Odense, Denmark)
TBA
String: Monday, 23/02/2026, 14:00, seminar room 226
Masahito Yamazaki (IPMU, University of Tokyo)
Emergent Symmetries in Ensemble Averages
In It has been a long-standing conjecture that any exact global symmetry should be broken in theories of quantum gravity. This statement, however, is not necessarily true one we consider ensemble averages in theories of quantum gravity. In this talk, we will discuss concrete setup of ensemble averages of Narain CFTs and their holographic duals, to discuss the emergence of global symmetries in ensemble averages. We can extract the essence of this correspondence, and discuss emergence of global theories in ensemble averages in general. Such phenomena is ubiquitous and is actually closely related to the concept of the strong-to-weak symmetry breaking, which has been attracting attention in condensed mattter / statistical physics literature recently.
Cosmo: Wednesday, 25/02/2026, 11:30, Lecture Hall
Vitor da Fonseca (University of Lisbona, Lisbona, Portugal)
TBA
Cosmo: Wednesday, 04/03/2026, 11:30, Lecture Hall
Alexandros Papageorgiou (IFT, Madrid, Spain)
TBA
String: Monday, 09/03/2026, 14:00, seminar room 226
Enrico Perron Cabus (Uppsala University, Uppsala, SWEDEN)
TBA
Cosmo: Wednesday, 11/03/2026, 11:30, Lecture Hall
Tays Miranda (Espirito Santo University, Brazil)
TBA
Cosmo: Wednesday, 18/03/2026, 11:30, Lecture Hall
Alberto Mangiagli (MPI, Potsdam, Germany)
TBA
Cosmo: Wednesday, 25/03/2026, 11:30, Lecture Hall
Carlos Herdeiro (Aveiro University, Aveiro, Portugal)
TBA
Cosmo: Wednesday, 01/04/2026, 11:30, Lecture Hall
Alessandra Silvestri (Leiden University, Leiden, Netherlands)
TBA
Cosmo: Wednesday, 08/04/2026, 11:30, Lecture Hall
Théo Simon (LUPM, Montpellier, France)
TBA
Cosmo: Wednesday, 15/04/2026, 11:30, Lecture Hall
Gabriella De Lucia (Trieste Observatory, Trieste, Italy)
TBA
Cosmo: Wednesday, 22/04/2026, 11:30, Lecture Hall
Clare Burrage (Nottingham University, Nottingham, UK)
TBA
Cosmo: Wednesday, 29/04/2026, 11:30, Lecture Hall
Gerasimos Rigopoulos (Newcastle University, Newcastle upon Tyne, UK)
TBA
Cosmo: Wednesday, 06/05/2026, 11:30, Lecture Hall
Laur Jarv (Tartu University, Tartu, Estonia)
TBA
Cosmo: Wednesday, 13/05/2026, 11:30, Lecture Hall
Jerôme Martin (IAP, Paris, France)
TBA