44187843
Linear Instability of Non-vacuum Spacetimes *
We study the problem of linear instability in non-vacuum spacetimes. For vacuum spa.cetimes linear instability occurs when the spacetime has Killing vectors. In the non-vacuum case, one must prescribe how the sources are to vary. For one natural choice, we show that the signal for instability is the existence of Integral Constraint Vector fields. These vector fields lead, as in the vacuum case, to nonlinear constraints on the first order perturbations to the metric and momentum. For other choices for variations of the sources, we show how to modify the definition of Integral Constra,int Vectors appropriately. Since Robertson-Walker spacetimes have Integral Constraint Vectors our results may have cosmological applications.
54006633
Dynamics of localized Kaluza-Klein black holes in a collapsing universe
The Clayton Antitrust Act of 1914 prohibits corporate mergers that would result in certain highly undesired end states. We study an exact solution of the Einstein equations describing localized, charged Kaluza?Klein black holes in a collapsing de Sitter universe and seek to demonstrate that a similar effect holds, preventing a potentially catastrophic black hole merger. As the collapse proceeds, it is natural to expect that the black hole undergoes a topological transition, wrapping around the shrinking compact dimension to merge with itself and form a black string. However, the putative uniform charged black string end state is singular and such a transition would violate (a reasonable notion of) cosmic censorship. We present analytic and numerical evidence that strongly suggests the absence of such a transition. Based on this evidence, we expect that the Kaluza?Klein black hole horizon stays localized, despite the increasingly constraining size of the compact dimension. On the other hand, the de Sitter horizon does change between spherical and cylindrical topologies in a simple way.
15094604
Conserved gravitational charges from Yano tensors
The defining properties of Yano tensors naturally generalize those of Killing vectors to anti-symmetric tensor fields of arbitrary rank. We show how the Yano tensors of flat spacetime can be used to construct new, conserved gravitational charges for transverse asymptotically flat spacetimes. The relationship of these new charges to Yano tensors parallels that of ordinary ADM conserved charges to Killing vectors. Hence, we call them Y-ADM charges. A rank n Y-ADM charge is given by an integral over a co-dimension n slice of spatial infinity. In particular, a rank (p+1) Y-ADM charge in a p-brane spacetime is given by an integral over only the sphere SD−(p+2) surrounding the brane and may be regarded as an intensive property of the brane.
9137125
Overlapping branes in M theory
We construct new supersymmetric solutions of D = 11 supergravity describing n orthogonally “overlapping” membranes and fivebranes for n = 2,…,8. Overlapping branes arise after separating intersecting branes in a direction transverse to all of the branes. The solutions, which generalize known intersecting brane solutions, preserve at least 2−n of the supersymmetry. Each pairwise overlap involves a membrane overlapping a membrane in a 0-brane, a fivebrane overlapping a fivebrane in a 3-brane or a membrane overlapping a fivebrane in a string. After reducing n overlapping membranes to obtain n overlapping D-2-branes in D = 10, T-duality generates new overlapping D-brane solutions in type IIA and type IIB string theory. Uplifting certain type IIA solutions leads to the D = 11 solutions. Some of the new solutions reduce to dilaton black holes in D = 4. Additionally, we present a D = 10 solution that describes two D-5-branes overlapping in a string. T-duality then generates further D = 10 solutions and uplifting one of the type IIA solutions gives a new D = 11 solution describing two fivebranes overlapping in a string.
7630417
U duality, D-branes, and black hole emission rates: Agreements and disagreements
An expression for the spacetime absorption coefficient of a scalar field in a five dimensional, near extremal black hole background is derived, which has the same form as that presented by Maldacena and Strominger, but is valid over a larger, U-duality invariant region of parameter space and in general disagrees with the corresponding D-brane result. We develop an argument, based on D-brane thermodynamics, which specifies the range of parameters over which agreement should be expected. For neutral emission, the spacetime and D-brane results agree over this range. However, for charged emission, we find disagreement in the ‘Fat Black Hole’ regime, in which charge is quantized in smaller units on the brane, than in the bulk of spacetime. We indicate a possible problem with the D-brane model in this regime. We also use the Born approximation to study the high frequency limit of the absorption coefficient and find that it approaches unity, for large black hole backgrounds, at frequencies still below the string scale, again in disagreement with D-brane results.
16666363
Do Killing-Yano tensors form a Lie algebra?
Killing–Yano tensors are natural generalizations of Killing vectors. We investigate whether Killing–Yano tensors form a graded Lie algebra with respect to the Schouten–Nijenhuis bracket. We find that this proposition does not hold in general, but that it does hold for constant curvature spacetimes. We also show that Minkowski and (anti)-deSitter spacetimes have the maximal number of Killing–Yano tensors of each rank and that the algebras of these tensors under the SN bracket are relatively simple extensions of the Poincare and (A)dS symmetry algebras.
3037493
Comment on "Perturbative stability of smooth strings"