# HEP – GR Seminar

Prof. S. Hollands
Prof. R. Verch

Organization:

Dr. A. Much

Dr. J. Zahn

Monday, 15:15 – 16:45 (1 hour talk, followed by questions), seminar room 114 ITP
» how to reach the ITP

This term, the seminar is held in a  virtual meeting room  (Passcode: 566288).

# Schedule for the summer term 2021:

Date Speaker Title (hover/click for abstract)
12.04.
19.04. Gerardo Morsella (Università di Roma)
26.04. Lucietti James (University of Edinburgh) Recording (Passcode: B.x557mj)
03.05. Fábio Novaes (Center for Scientific Studies, Valdivia)
10.05. Marco Merkli (Memorial University of Newfoundland)         See arxiv articles 1, 2.
17.05. Alessio Ranallo (University of Rome Tor Vergata)
31.05. Leon Deryck Loveridge (University of South-Eastern Norway)
07.06.
14.06. Markus Fröb (University of Leipzig)
21.06.
28.06. Mark M. Wilde (Louisiana State University)
05.07. Marco Merkli (Memorial University of Newfoundland)         See arxiv articles 1, 2.
12.07. Daniel Roggenkamp (University of Mannheim)
19.07. Nima Lashkari (Purdue University)

## Schedules of past terms:

Abstract:
Abstract: Local QFT on Doplicher-Fredenhagen-Roberts quantum spacetime is equivalent to a non-local QFT on ordinary (commutative) spacetime, which has quite generally a better UV behavior in perturbation theory, but for which the control of the adiabatic limit is problematic. I will show that the adaptation of the methods of perturbative QFT, originally developed for local QFT on ordinary spacetimes, to QFT on quantum spacetime yields a non-local UV-finite theory which enjoys some remnants of causality. This is sufficient to prove the existence of the adiabatic limit of vacuum expectation values of interacting observables. (Joint work with S. Doplicher and N. Pinamonti.)
Abstract: The classification of stationary black hole solutions is a major open problem in higher-dimensional General Relativity. I will report on recent progress towards this problem for five-dimensional, asymptotically flat, vacuum black holes with biaxial symmetry. It is well known that the Einstein equations for this class of spacetimes arise as the integrability condition of an auxiliary linear system. I will show that the general solution to the Belinski-Zakharov linear system on the axes and horizons determines the metric data there in terms of a set of moduli that must satisfy certain algebraic equations. In particular, this is sufficient to determine the moduli space of solutions that are free of conical singularities on the axes.  As examples, we obtain constructive uniqueness proofs for the Myers-Perry black holes and the known doubly spinning black rings. We also use this method to demonstrate the nonexistence of the simplest class of black holes with lens space horizon topology.
Abstract: Understanding deeply the scattering properties of black holes is crucial to decode  gravitational waves signals. In this talk, we present the isomonodromic approach to obtain quasinormal modes from linear perturbations of exact black hole solutions, focusing on the Kerr-de Sitter metric. This approach is grounded on recent advances in integrable systems and conformal field theory, which we will also review. Finally, we will briefly highlight other applications of the isomonodromic method in CFT, conformal mappings and quantum optics.
Abstract: We consider a bipartite quantum system in which a small part ("the system") interacts with a large part ("the reservoir"). Due to their interaction, the dynamics of the system has a very complicated structure. A central task in the theory of open quantum systems is to find simpler, approximate equations for the system dynamics, in particular the ubiquitous Markovian master equation. The propagator of this equation is a semi-group in time, generated by a complex Hamiltonian', allowing for oscillations and decay in the dynamics. The Markovian approximation should hold if the system-reservoir interaction is not too strong and if the reservoir has a short memory time. Its validity, supported by heuristic and numerical studies, is accepted and used in all quantum sciences. Davies in the mid 70ies gave a proof of the correctness of the approximation for times not too large (weak coupling, van Hove limit). Based on a quantum resonance theory, we have recently shown that the Markovian approximation is valid for all time-scales, with a controllable error between the true and the approximate dynamics. The goal of the talk is to outline these results and the ideas behind the proofs.
Abstract: In this talk, I will present some recent results concerning the entropy carried by Klein-Gordon waves on curved backgrounds. After a quick introduction to the formalisation scheme, introduced in a previous work by Ciolli, Longo, and Ruzzi, I will continue presenting some known results in AQFT on curved spacetimes. Finally, I will show how to apply the aforementioned scheme to this more general case. Joint work with Fabio Ciolli, Roberto Longo, and Giuseppe Ruzzi.
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Abstract: We consider a bipartite quantum system in which a small part ("the system") interacts with a large part ("the reservoir"). Due to their interaction, the dynamics of the system has a very complicated structure. A central task in the theory of open quantum systems is to find simpler, approximate equations for the system dynamics, in particular the ubiquitous Markovian master equation. The propagator of this equation is a semi-group in time, generated by a complex Hamiltonian', allowing for oscillations and decay in the dynamics. The Markovian approximation should hold if the system-reservoir interaction is not too strong and if the reservoir has a short memory time. Its validity, supported by heuristic and numerical studies, is accepted and used in all quantum sciences. Davies in the mid 70ies gave a proof of the correctness of the approximation for times not too large (weak coupling, van Hove limit). Based on a quantum resonance theory, we have recently shown that the Markovian approximation is valid for all time-scales, with a controllable error between the true and the approximate dynamics. The goal of the talk is to outline these results and the ideas behind the proofs.
Abstract:
Abstract: The forgetful and entanglement-breaking quantum channels play an important role in error correction. I discuss the physical realization of these channels that disentangle regions of spacetime in quantum field theory. In holographic theories, as we increase the separation of two disjoint regions a phase transition occurs making the mutual information vanish at some finite distance. I comment on the relation between this transition and the formation of islands during black hole evaporation.