# 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**. Unless explicitly stated otherwise, the regular (not-lunch) relativity seminars take place in Room 218 **2nd floor, Währingerstrasse 17.**

The Mathematical Physics Seminars take place on Tuesdays at 14.15.

The Particle Physics Seminars take place on Tuesdays at 16.15.

- Friday,
**August 3rd**, 13:00, Todd Oliynyk (Monash University, Australia):*Dynamical relativistic liquid bodies*

Abstract: In this talk, I will discuss a new approach to establishing the well-posedness of the relativistic Euler equations for liquid bodies in vacuum. The approach is based on a wave formulation of the relativistic Euler equations that consists of a system of non-linear wave equations in divergence form together with a combination of acoustic and Dirichlet boundary conditions. The equations and boundary conditions of the wave formulation differs from the standard one by terms proportional to certain constraints, and one of the main technical problems to overcome is to show that these constraints propagate, which is necessary to ensure that solutions of the wave formulation determine solutions to the Euler equations with vacuum boundary conditions. During the talk, I will describe the derivation of the wave equation and boundary conditions, the origin of the constraints, and how one shows that the constraints propagate. Time permitting, I will also discuss how energy estimates can be obtained from this new formulation paying particular attention to the role of the acoustic boundary conditions.

- Thursday,
**August 16th, 14:00, Seminarraum A**

On the occasion of the approaching 70th Birthday of Bobby Beig, we are pleased to invite you to a talk by Walter Simon (Univ. Vienna):*The Beig-Krammer tensor on the three sphere*

Abstract: Motivated by the conformal method of solving the constraints in General Relativity, R. Beig and W. Krammer defined, on any 3-dimensional conformally flat Riemannian manifold M, a symmetric, tracefree two-tensor as the tensor product of an arbitrary vector V and a conformal Killing vector W.

If V is divergence free, so is the Beig-Krammer tensor - hence it can serve as ADM momentum density in vacuum, (possibly with cosmological constant).

We examine the very special case that M is the round three sphere and that V and W are Killing vectors, and compare with the known "donut" case.

The application of this tensor to the initial value problem becomes particulary interesting in view of a recent theorem by Premoselli which in essence settles the question of (non-)existence of solutions of the Lichnerowicz equation on compact Riemannian three manifolds.

This is joint and ongoing work with Piotr Bizon.