# Current seminars

In addition to the Vienna relativity seminars, the calendar above sometimes contains other events of interest to members of the relativity group. The seminars of the Vienna relativity group are listed below.

Location (unless indicated otherwise): Währinger Str. 17

- Room 218 on the 2nd floor for **standard seminars**, and

- Common room, first floor, for **lunch seminars**.

The Mathematical Physics Seminars take place on Tuesdays at 13.45.

The Particle Physics Seminars take place on Tuesdays at 16.15.

- Monday,
**January 28th**, 13:00, lunch seminar

Zoe Wyatt (Edinburgh and Univ. Vienna):*An introduction to the r*^{p}-weighted vector field method of Dafermos and Rodnianski

Abstract: In 2009 Dafermos and Rodnianski introduced a new approach to decay estimates of wave equations on a Lorentzian background. Instead of using global vector field multipliers and commutators with weights in t, they developed a heirarchy of estimates coming from r^{p} weighted vector fields. In this talk I will introduce their method applied to Minkowski and Schwarzschild spacetimes and outline some of the reasons why their method is particularly useful when dealing with Schwarzschild and Kerr background metrics. SC005336.

- Thursday, January 31st, 14:00, Seminarraum A

Zoe Wyatt (Edinburgh and Vienna):*Attractors of the Einstein-Klein-Gordon system*

Abstract: The Milne cosmological model, a specific case of the FLRW family of cosmologies, represents an expanding universe emanating from a big bang singularity with a linear scale factor. With such a slow expansion rate, particularly compared to related isotropically expanding models (such as de Sitter), there are interesting questions one can ask about stability of this spacetime. For example previous results have shown that, when looking at the initial value problem, the Milne model is a stable solution to the vacuum Einstein, Einstein-Klein-Gordon and Einstein-Vlasov systems. Motivated by the last result, I will discuss our proof of the stability of the Milne model to the Einstein-Klein-Gordon system. This was shown recently by J. Wang using an alternative gauge and method. Thus I will also give comparisons between our method and results. This is joint work with D. Fajman.

- Thursday, March 28th (as part of the joint relativity-geometric analysis seminar), 13:30, Seminarraum A

Simon Raulot (Rouen):*Yamabe invariants and Cheeger constant on Poincaré-Einstein manifolds*

Abstract: In the first part of this talk, we present an elementary proof of the rigidity of the hyperbolic space as the unique Poincaré-Einstein manifold whose boundary at infinity is the conformal round sphere. The proof relies on an inequality which relates the Yamabe invariant of the boundary with the one of a compactification of the bulk manifold. In a second part, we relate the Cheeger constant of such manifolds with the conformal type of the boundary at infinity . More precisely, we prove that this constant is exactly the dimension of the interior of the Poincaré-Einstein manifold if and only if the Yamabe invariant of the boundary is non negative. Several applications are then discussed.