64 research outputs found
Instabilities in Higher-Dimensional Theories of Gravity
A number of models of nature incorporate dimensions beyond our observed four. In this thesis 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 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. 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 particular, 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
Bouncing Cosmology in Three Dimensions
We consider a dynamical two-brane in a four dimensional black hole background
with scalar hair. At high temperature this black hole goes through a phase
transition by radiating away the scalar. The end phase is a topological
adS-Schwarzschild black hole. We argue here that for a sufficiently low
temperature, the brane motion in this geometry is non-singular. This results in
a universe which passes over from a contracting phase to an expanding one
without reaching a singularity.Comment: 7 pages, LaTex, 3 figures, Journal versio
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
Born-Infeld black holes in the presence of a cosmological constant
We construct asymptotically anti-deSitter (and deSitter) black hole solutions
of Einstein-Born-Infeld theory in arbitrary dimension. We critically analyse
their geometries and discuss their thermodynamic properties.Comment: 10 Pages, 6 Figures, LaTeX, to appear in Phys. Letts.
Domain Wall Dynamics in Brane World and Non-singular Cosmological Models
We study brane cosmology as 4D (4-dimensional) domain wall dynamics in 5D
bulk spacetime. For a generic 5D bulk with 3D maximal symmetry, we derive the
equation of motion of a domain wall and find that it depends on mass function
of the bulk spacetime and the energy-momentum conservation in a domain wall is
affected by a lapse function in the bulk. Especially, for a bulk spacetime with
non-trivial lapse function, energy of matter field on the domain wall goes out
or comes in from the bulk spacetime. Applying our result to the case with SU(2)
gauge bulk field, we obtain a singularity-free universe in brane world
scenario, that is, not only a big bang initial singularity of the brane is
avoided but also a singularity in a 5D bulk does not exist.Comment: 12 pages, 11 figures, submitted to PRD. One reference is added. (v2
Bouncing cosmological solutions and their stability
In the present paper we consider the bouncing braneworld scenario, in which
the bulk is given by a five-dimensional charged AdS black hole spacetime with
matter field confined in a brane. Then, we study the stability of
solutions with respect to homogeneous and isotropic perturbations.
Specifically, the AdS black hole with zero ADM mass and charge, and open
horizon is an attractor, while the charged AdS black hole with zero ADM mass
and flat horizon, is a repeller.Comment: 9 pages, 1 figur
Bouncing cosmological solutions due to the self-gravitational corrections and their stability
In this paper we consider the bouncing braneworld scenario, in which the bulk
is given by a five-dimensional AdS black hole spacetime with matter field
confined in a brane. Exploiting the CFT/FRW-cosmology relation, we
consider the self-gravitational corrections to the first Friedmann-like
equation which is the equation of the brane motion. The self-gravitational
corrections act as a source of stiff matter contrary to standard FRW cosmology
where the charge of the black hole plays this role. Then, we study the
stability of solutions with respect to homogeneous and isotropic perturbations.
Specifically, if we do not consider the self-gravitational corrections, the AdS
black hole with zero ADM mass, and open horizon is an attractor, while, if we
consider the self-gravitational corrections, the AdS black hole with zero ADM
mass and flat horizon, is a repellerComment: 9 pages, no figure
Generalized Holographic Cosmology
We consider general black hole solutions in five-dimensional spacetime in the
presence of a negative cosmological constant. We obtain a cosmological
evolution via the gravity/gauge theory duality (holography) by defining
appropriate boundary conditions on a four-dimensional boundary hypersurface.
The standard counterterms are shown to renormalize the bare parameters of the
system (the four-dimensional Newton's constant and cosmological constant). We
discuss the thermodynamics of cosmological evolution and present various
examples. The standard brane-world scenarios are shown to be special cases of
our holographic construction.Comment: 15 pages, 5 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
Stability Analysis of Superconducting Electroweak Vortices
We carry out a detailed stability analysis of the superconducting vortex
solutions in the Weinberg-Salam theory described in Nucl.Phys. B826 (2010) 174.
These vortices are characterized by constant electric current and electric
charge density , for they reduce to Z strings. We consider the
generic field fluctuations around the vortex and apply the functional Jacobi
criterion to detect the negative modes in the fluctuation operator spectrum. We
find such modes and determine their dispersion relation, they turn out to be of
two different types, according to their spatial behavior. There are
non-periodic in space negative modes, which can contribute to the instability
of infinitely long vortices, but they can be eliminated by imposing the
periodic boundary conditions along the vortex. There are also periodic negative
modes, but their wavelength is always larger than a certain minimal value, so
that they cannot be accommodated by the short vortex segments. However, even
for the latter there remains one negative mode responsible for the homogeneous
expansion instability. This mode may probably be eliminated when the vortex
segment is bent into a loop. This suggests that small vortex loops balanced
against contraction by the centrifugal force could perhaps be stable.Comment: 42 pages, 11 figure
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