Conformal geodesics on vacuum space-times

We discuss properties of conformal geodesics on general, vacuum, and warped product space-times and derive a system of conformal deviation equations. The results are used to show how to construct on the Schwarzschild-Kruskal space-time global conformal Gauss coordinates which extends smoothly and without degeneracy to future and past null infinity

Einstein's equation and geometric asymptotics

The intimate relations between Einstein's equation, conformal geometry, geometric asymptotics, and the idea of an isolated system in general relativity have been pointed out by Penrose many years ago. A detailed analysis of the interplay of conformal geometry with Einstein's equation allowed us to deduce from the conformal properties of the field equations a method to derive under various assumptions definite statements about the feasibility of the idea of geometric asymptotics. More recent investigations have demonstrated the possibility to analyse the most delicate problem of the subject -- the behaviour of asymptotically flat solutions to Einstein's equation in the region where ``null infinity meets space-like infinity'' -- to an arbitrary precision. Moreover, we see now that the, initially quite abstract, analysis yields methods for dealing with practical issues. Numerical calculations of complete space-times in finite grids without cut-offs become feasible now. Finally, already at this stage it is seen that the completion of these investigations will lead to a clarification and deeper understanding of the idea of an isolated system in Einstein's theory of gravitation. In the following I wish to give a survey of the circle of ideas outlined above, emphasizing the interdependence of the structures and the naturalness of the concepts involved.Comment: Plenary lecture on mathematical relativity at the GR15 conference, Poona, Indi

The Taylor expansion at past time-like infinity

We study the initial value problem for the conformal field equations with data given on a cone ${\cal N}_p$ with vertex $p$ so that in a suitable conformal extension the point $p$ will represent past time-like infinity $i^-$, the set ${\cal N}_p \setminus \{p\}$ will represent past null infinity ${\cal J}^-$, and the freely prescribed (suitably smooth) data will acquire the meaning of the incoming {\it radiation field} for the prospective vacuum space-time. It is shown that: (i) On some coordinate neighbourhood of $p$ there exist smooth fields which satisfy the conformal vacuum field equations and induce the given data at all orders at $p$. The Taylor coefficients of these fields at $p$ are uniquely determined by the free data. (ii) On ${\cal N}_p$ there exists a unique set of fields which induce the given free data and satisfy the transport equations and the inner constraints induced on ${\cal N}_p$ by the conformal field equations. These fields and the fields which are obtained by restricting the functions considered in (i) to ${\cal N}_p$ coincide at all orders at $p$.Comment: 40 page

Static vacuum solutions from convergent null data expansions at space-like infinity

We study formal expansions of asymptotically flat solutions to the static vacuum field equations which are determined by minimal sets of freely specifyable data referred to as `null data'. These are given by sequences of symmetric trace free tensors at space-like infinity of increasing order. They are 1:1 related to the sequences of Geroch multipoles. Necessary and sufficient growth estimates on the null data are obtained for the formal expansions to be absolutely convergent. This provides a complete characterization of all asymptotically flat solutions to the static vacuum field equations.Comment: 65 page

Geometric Asymptotics and Beyond

We discuss some global and semi-global existence and stability results obtained with the use of the conformal field equations.Comment: 34 page

Spin-2 fields on Minkowski space near space-like and null infinity

We show that the spin-2 equations on Minkowski space in the gauge of the `regular finite initial value problem at space-like infinity' imply estimates which, together with the transport equations on the cylinder at space-like infinity, allow us to obtain for a certain class of initial data information on the behaviour of the solution near space-like and null infinity of any desired precision.Comment: 18 page

On the non-linearity of the subsidiary systems

In hyperbolic reductions of the Einstein equations the evolution of gauge conditions or constraint quantities is controlled by subsidiary systems. We point out a class of non-linearities in these systems which may have the potential of generating catastrophic growth of gauge resp. constraint violations in numerical calculations.Comment: 7 page

On the AdS stability problem

We discuss the notion of stability and the choice of boundary conditions for AdS-type space-times and point out difficulties in the construction of Cauchy data which arise if reflective boundary conditions are imposed.Comment: 12 page

Asymptotically Flat Initial Data with Prescribed Regularity at Infinity

We prove the existence of a large class of asymptotically flat initial data with non-vanishing mass and angular momentum for which the metric and the extrinsic curvature have asymptotic expansions at space-like infinity in terms of powers of a radial coordinate.Comment: Latex 2e, 47 pages, no figure