Taking place bi-weekly on Fridays at 15:00 starting November 2022.

The organizers are Marc Casals, Stefan Czimek and Dejan Gajic.

Location: Either Mathematical Institute or Institute for Theoretical Physics, announced with each talk.

This seminar series is part of the Center for Mathematical Physics in Leipzig.

- Friday, January 20th, 2023, 15:00:
**Aaron Kovacs**.- Title: On the Cauchy problem in Effective Field Theories of gravity
- Abstract: Effective field theory provides a way of parameterizing strong-field deviations from General Relativity that might be observable in the gravitational waves emitted in a black hole merger. To perform numerical simulations of black hole mergers in such theories it is necessary that the equations be written in a form that admits a well-posed initial value formulation. In this talk, I will discuss recent progress in the initial value formulation of effective theories of gravity, as well as some open problems.
- Location: ITP, seminar room 114

- Thursday, January 19th, 2023, 15:00:
**Georgios Moschidis**(EPFL).- Title: Turbulence in general relativity
- Abstract: In the presence of confinement, the Einstein field equations are expected to exhibit turbulent dynamics. One way to introduce confinement to the equations is by imposing a negative value for the cosmological constant and study the evolution of solutions with Anti-de Sitter asymptotics. In this talk, we will focus on two settings where turbulence emerges in the dynamics of the Einstein equations. First, in the case of small perturbations of Anti de-Sitter spacetime, we will establish the AdS instability conjecture for the spherically symmetric Einstein-scalar field system. We will, then, proceed to show how weak turbulence arises in a quasilinear toy model for the vacuum Einstein equations in the exterior of a Schwarzschild-AdS black hole. This is joint work with Christoph Kehle.
- Location:
**Oberseminar Analysis**, Mathematisches Institut, A314.

- Friday, December 9th, 2022, 15:00:
**Leonhard Kehrberger**.- Title: The Case Against Smooth Null Infinity
- Abstract: Penrose's proposal of smooth conformal compactification is not only of geometric elegance, it also has concrete, physical implications, such as the "peeling off" of gravitational radiation near infinity. One natural question to ask is then: Do physically relevant spacetimes admit a smooth conformal compactification? To answer this question, I will present a scattering construction of spacetimes describing the far region of $N$ infalling masses coming from the infinite past and following approximately Keplerian orbits, and prove that such spacetimes violate the "peeling property" both in the past and in the future. This violation is in principle measurable in the form of leading-order deviations from the usual late-time tails of gravitational radiation.
- Location: ITP, seminar room 114

- Wednesday, November 23rd, 2022, 11:00:
**Alexandre Le Tiec**.- Title: The shape of black hole Love
- Location: ITP, seminar room 114

- Thursday, November 17th, 2022, 15:00:
**Dawei Shen**.- Title: General covariant modulated (GCM) procedure
- Abstract: I will start by introducing the main idea of the proof of the “Kerr stability for small angular momentum” by Klainerman and Szeftel, as our motivation to introduce the General Covariant Modulated (GCM) procedure. Then, I will present the paper “Constructions of GCM spheres in perturbations of Kerr” of Klainerman and Szeftel concerning the construction of GCM spheres. Finally, by applying the GCM spheres I will explain the main result concerning the “Constructions of GCM hypersurfaces in perturbations of Kerr”.
- Location: zoom

- Friday, November 11th, 2022, 15:00:
**Stefan Hollands**.- Title: Perturbation Theory in Kerr Spacetime
- Abstract: I review some recent developments in the perturbation theory of Kerr - and more generally Petrov type D - spacetimes: The GHZ method has opened the way to use the so-called metric reconstruction procedure to construct metric perturbations satisfying the sourced linearized Einstein equations with generic sources, while at the same time taking advantage of the highly special features of type D spacetime. The procedure can be thought of as a generalization of the well-known and widely used metric reconstruction procedure due originally to Chrzanowski, Kohen, and Kegeles (CCK), which however only works for the vacuum Einstein equations and thereby very severely limits its use for practical applications such as the gravitation self-force problem. The key new ideas is to include a suitable corrector tensor into the CCK ansatz which is determined by a set of simple transport type equations. I review related results on an infinite set of conserved currents for metric-, electromagnetic- or scalar perturbations of Kerr containing $2n+1+2s$ derivatives. These currents, like the separability property of the Teukolsky equation underlying the reconstruction scheme, are related to the "Killing tensor" that exists in Petrov type D spacetimes.
- Location: ITP, seminar room 114