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

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 $D_3$ 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

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

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

Non-uniform Black Strings with Schwarzschild-(Anti-)de Sitter Foliation

We present some exact non-uniform black string solutions of 5-dimensional pure Einstein gravity as well as Einstein-Maxwell-dilaton theory at arbitrary dilaton coupling. The solutions share the common property that their 4-dimensional slices are Schwarzchild-(anti-)de Sitter spacetimes. The pure gravity solution is also generalized to spacetimes of dimensions higher than 5 to get non-uniform black branes.Comment: LaTeX 14 pages, 3 eps figures. V2: version appeared in CQ

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

A Matrix Model for the Null-Brane

The null-brane background is a simple smooth 1/2 BPS solution of string theory. By tuning a parameter, this background develops a big crunch/big bang type singularity. We construct the DLCQ description of this space-time in terms of a Yang-Mills theory on a time-dependent space-time. Our dual Matrix description provides a non-perturbative framework in which the fate of both (null) time, and the string S-matrix can be studied.Comment: 26 pages, LaTeX; references adde

A Matrix Big Bang

The light-like linear dilaton background represents a particularly simple time-dependent 1/2 BPS solution of critical type IIA superstring theory in ten dimensions. Its lift to M-theory, as well as its Einstein frame metric, are singular in the sense that the geometry is geodesically incomplete and the Riemann tensor diverges along a light-like subspace of codimension one. We study this background as a model for a big bang type singularity in string theory/M-theory. We construct the dual Matrix theory description in terms of a (1+1)-d supersymmetric Yang-Mills theory on a time-dependent world-sheet given by the Milne orbifold of (1+1)-d Minkowski space. Our model provides a framework in which the physics of the singularity appears to be under control.Comment: 25 pages, LaTeX; v2: discussion of singularity of Einstein frame metric added, references adde

On Bouncing Brane-Worlds, S-branes and Branonium Cosmology

We present several higher-dimensional spacetimes for which observers living on 3-branes experience an induced metric which bounces. The classes of examples include boundary branes on generalised S-brane backgrounds and probe branes in D-brane/anti D-brane systems. The bounces we consider normally would be expected to require an energy density which violates the weak energy condition, and for our co-dimension one examples this is attributable to bulk curvature terms in the effective Friedmann equation. We examine the features of the acceleration which provides the bounce, including in some cases the existence of positive acceleration without event horizons, and we give a geometrical interpretation for it. We discuss the stability of the solutions from the point of view of both the brane and the bulk. Some of our examples appear to be stable from the bulk point of view, suggesting the possible existence of stable bouncing cosmologies within the brane-world framework.Comment: 35 pages, 7 figures, JHEP style. Title changed and references 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