122310749
Perturbations of Friedmann-Robertson-Walker cosmological models
The mathematical principles underlying the theory of gauge-invariant perturbations of homogeneous isotropic cosmological models are discussed and a collection of useful formulae is given.
122328013
Spherically symmetric thin domain walls
Domain walls for a simple model of a scalar field coupled to gravity are investigated in the thin-wall approximation. When gravity is not present it is known that spherically symmetric domain walls minimise the Euclidean action. A corresponding result for gravitational interactions has not been found. Here some conditions sufficient to guarantee spherically symmetric configurations are established. Relaxing them could lead to toroidal bubbles, which are probably unstable.
122922344
A simple model for radiation damping
Increasing interest has been shown in the method of matched asymptotic expansions for the construction and solution of the equations of motion in general relativity. This paper discusses a simple model which can, in principle, be solved exactly. A comparison of the two solutions shows that the matched asymptotic expansion technique determines correctly the final damping rate and frequency (at least to fourth order in a small parameter), but the phase information is spurious.
119398612
Naked and Thunderbolt Singularities in Black Hole Evaporation
If an evaporating black hole does not settle down to a non radiating remnant, a description by a semi classical Lorentz metric must contain either a naked singularity or what we call a thunderbolt, a singularity that spreads out to infinity on a spacelike or null path. We investigate this question in the context of various two dimensional models that have been proposed. We find that if the semi classical equations have an extra symmetry that make them solvable in closed form, they seem to predict naked singularities but numerical calculations indicate that more general semi classical equations, such as the original CGHS ones give rise to thunderbolts. We therefore expect that the semi classical approximation in four dimensions will lead to thunderbolts. We interpret the prediction of thunderbolts as indicating that the semi classical approximation breaks down at the end point of black hole evaporation, and we would expect that a full quantum treatment would replace the thunderbolt with a burst of high energy particles. The energy in such a burst would be too small to account for the observed gamma ray bursts.
122787969
Characteristic initial data and wavefront singularities in general relativity
The structure of singularities (caustics), self-intersections of wavefronts (null hypersurfaces) and wavefront families (null coordinates) in arbitrary space-times is discussed in detail and illustrated by explicit examples of stable wavefront singularities in Minkowski space. It is shown how characteristic initial data determine the caustics and the self-intersections of the characteristics of Einstein’s field equations.
17101492
Continuous self-similarity and S-duality
We study the spherically symmetric collapse of the axion/dilaton system coupled to gravity. We show numerically that the critical solution at the threshold of black hole formation is continuously self-similar. Numerical and analytical arguments both demonstrate that the mass scaling away from criticality has a critical exponent of .
118364186
Measurement of Spin Effects in pp Elastic Scattering Using the Polarized Beam at the AGS
Using the recently developed 18.5 GeV/c AGS polarized proton beam and a polarized proton target we measured the analyzing power, A, and the spin-spin correlation parameter, Ann, in medium-P2 ⊥ proton-proton elastic scattering. We found sharp dips in both A and Ann, which occur at different P2 ⊥ values. The unexpected sharp structure in the spin-spin force occurs near P2 ⊥ = 2.3 [GeV/c]2 where the elastic cross-section has no apparent structure.
121463461
Overcoming depolarizing resonances with a Siberian snake