Forthcoming events in this series


Tue, 13 Nov 2007
11:00
L3

Static vacuum data and their conformal classes

Helmut Friedrich
(Allbert Einstein Institute)
Abstract

Static vacuum data and their conformal classes play an important role in the discussion of the smoothness of gravitational fields at null infinity. We study the question under which conditions such data admit non-trivial conformal rescalings which lead again to such data. Some of the restrictions implied by this requirement are discussed and it is shown that there exists a 3-parameter family of static vacuum data which are not conformally flat and which admit non-trivial rescalings.

Tue, 30 Oct 2007
11:00
L3

Towards a proof of a rigidity conjecture for asymptotically flat spacetimes

Juan Valiente Kroon
(Queen Mary College, London)
Abstract

I will discuss ongoing work to provide a proof for the following

conjecture: if the development of a time symmetric, conformally flat

initial data set admits a smooth null infinity, then the initial data

is Schwarzschildean in a neighbourhood of infinity. The strategy

to construct a proof consists in a detailed analysis of a

certain type of expansions that can be obtained using H. Friedrich's

"cylinder at infinity" formalism. I will also discuss a toy model for

the analysis of the Maxwell field near the

spatial infinity of the Schwarzschild spacetime

Tue, 09 Oct 2007
12:00
L3

The classification of higher-dimensional black holes

Stefan Hollands
Abstract
It has been known for some time that in more than 4 spacetime dimensions, there is a considerably larger variety of black "hole" solutions, having e.g. different horizon topology. In particular, they are no longer fully characterized by their asymptotic charges (mass, angular momenta) alone. We give a partial classification theorem for higher dimensions, for solutions with sufficiently many axial Killing fields. We show that higher dimensional black holes may be fully characterized by their asymptotic charges, together with certain "moduli" and "winding numbers" that are analogous to those of Seiffert fibrations. In particular, we find constraints on the possible horizon topologies. In 5 dimensions, they may be either a black "hole" (sphere), black "ring", or a black "lens".
Tue, 29 May 2007
12:00
L3

Logarithmic Frobenius structures

Misha Feigin
(Glasgow)
Abstract
  I am going to discuss a special class of logarithmic solutions to WDVV equations. This type of solutions appeared in Seiberg-Witten theory is defined by a finite set of covectors, the V-systems. The V-systems introduced by Veselov have remarkable properties. They contain Coxeter root systems, and they are closed under taking subsystems and restrictions. The corresponding solutions are almost dual in Dubrovin's sense to the Frobenius manifolds structures on the orbit spaces of Coxeter groups and their restrictions to discriminants. Another source of V-systems is generalized root systems. The talk will be based on joint work with Veselov.    
Tue, 15 May 2007
12:00
L3

Polarized and half polarized U(1) symmetric vacuum spacetimes with AVTD behaviour.

Yvonne Choquet Bruhat
(Universite Pierre & Marie Curie)
Abstract
    I sketch, using Kichenassamy - Rendall ideas, a simplified and generalized proof of the Fuchs theorem for differential equations with a singularity. I use the theorem to construct solutions of polarized and half polarized U(1) symmetric vacuum spacetimes with "Asymptotically Velocity Terms Dominated" (AVTD) behaviour near the singularity. I show that the definition I give of half polarization for U(1) symmetric vacuum space-times is a necessary and sufficient condition for non polarized such spacetimes to have this AVTD behaviour.  
Tue, 27 Feb 2007
12:00
L3

J vs m

Piotr Chrusciel
(Oxford)
Abstract
  We will shortly review the known bounds on the angular momentum J in terms of mass m assuming a negative cosmological constant, and describe in more detail Brill's proof of the axisymmetric positive energy theorem, and Dain's upper bound on angular momentum J for vacuum initial data sets with an axial Killing vector and with two asymptotically flat regions.