4 research outputs found
Black Rings, Boosted Strings and Gregory-Laflamme
We investigate the Gregory-Laflamme instability for black strings carrying
KK-momentum along the internal direction. We demonstrate a simple kinematical
relation between the thresholds of the classical instability for the boosted
and static black strings. We also find that Sorkin's critical dimension depends
on the internal velocity and in fact disappears for sufficiently large boosts.
Our analysis implies the existence of an analogous instability for the
five-dimensional black ring of Emparan and Reall. We also use our results for
boosted black strings to construct a simple model of the black ring and argue
that such rings exist in any number of space-time dimensions.Comment: 26 pages, 6 figure
Instability of non-supersymmetric smooth geometries
Recently certain non-supersymmetric solutions of type IIb supergravity were
constructed [hep-th/0504181], which are everywhere smooth, have no horizons and
are thought to describe certain non-BPS microstates of the D1-D5 system. We
demonstrate that these solutions are all classically unstable. The instability
is a generic feature of horizonless geometries with an ergoregion. We consider
the endpoint of this instability and argue that the solutions decay to
supersymmetric configurations. We also comment on the implications of the
ergoregion instability for Mathur's `fuzzball' proposal.Comment: v2: typos corrected, reference adde
Bouncing Braneworlds Go Crunch!
Recently, interesting braneworld cosmologies in the Randall-Sundrum scenario
have been constructed using a bulk spacetime which corresponds to a charged AdS
black hole. In particular, these solutions appear to `bounce', making a smooth
transition from a contracting to an expanding phase. By considering the
spacetime geometry more carefully, we demonstrate that generically in these
solutions the brane will encounter a singularity in the transition region.Comment: 17 pages, 4 figures, ref adde
INSTABILITIES IN HIGHER-DIMENSIONAL THEORIES OF GRAVITY
author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. ii A number of models of nature incorporate dimensions beyond our observed four. In this the-sis we examine some examples and consequences of classical instabilities that emerge in the higher-dimensional theories of gravity which can describe their low energy phenomenology. We first investigate a gravitational instability for black strings carrying momentum along an internal direction. We argue that this implies a new type of solution that is nonuniform along the extra dimension and find that there is a boost dependent critical dimension for which they are stable. Our analysis implies the existence of an analogous instability for the five-dimensional black ring. We construct a simple mode of the black ring to aid in applying these results and argue that such rings should exist in any number of space-time dimensions. Next we consider a recently constructed class of nonsupersummetric solutions of type IIB supergravity which are everywhere smooth and have no horizon. We demonstrate that these solutions are all classically unstable. The instability is a generic feature of horizonless ge-ometries with an ergoregion. We consider the endpoint of this instability and argue that the solutions decay to supersymmetric configurations. We also comment on the implications of the ergoregion instability for Mathur’s ‘fuzzball ’ proposal. Finally, we consider an interesting braneworld cosmology in the Randall-Sundrum scenario constructed using a bulk space-time which corresponds to a charged AdS black hole. In partic-ular, these solutions appear to ‘bounce’, making a smooth transition from a contracting to an expanding phase. By considering the space-time geometry more carefully, we demonstrate that generically in these solutions the brane will encounter a singularity in the transition region. ii