Open String Creation by S-Branes

An sp-brane can be viewed as the creation and decay of an unstable D(p+1)-brane. It is argued that the decaying half of an sp-brane can be described by a variant of boundary Liouville theory. The pair creation of open strings by a decaying s-brane is studied in the minisuperspace approximation to the Liouville theory. In this approximation a Hagedorn-like divergence is found in the pair creation rate, suggesting the s-brane energy is rapidly transferred into closed string radiation.Comment: Talk presented at the Hangzhou String 2002 Conference, August 12-1

Non-Standard Intersections of S-Branes in D=11 Supergravity

We construct new intersecting S-brane solutions in 11-dimensional supergravity which do not have supersymmetric analogs. They are obtained by letting brane charges to be proportional to each other. Solutions fall into two categories with respect to whether there is a non-diagonal term to be cancelled in the field equations or not. In each case we show that they can be constructed by using a simple set of rules which is similar to the harmonic function rule of the usual static p-branes. Furthermore, we study an intersection where the Chern-Simons term makes a non-zero contribution to the field equations. We show that this configuration has a singularity like other S-branes.Comment: 13 pages, 2 figures;v2 Section 2.2 is improved with new examples, references added;v3 typos correcte

Intersecting S-Brane Solutions of D=11 Supergravity

We construct all possible orthogonally intersecting S-brane solutions in 11-dimensions corresponding to standard supersymmetric M-brane intersections. It is found that the solutions can be obtained by multiplying the brane and the transverse directions with appropriate powers of two hyperbolic functions of time. This is the S-brane analog of the ``harmonic function rule''. The transverse directions can be hyperbolic, flat or spherical. We also discuss some properties of these solutions.Comment: 12 pages, Latex, a reference adde

On Winding Branes and Cosmological Evolution of Extra Dimensions in String Theory

We consider evolution of compact extra dimensions in cosmology and try to see whether wrapped branes can prevent the expansion of the internal space. Some difficulties of Brandenberger and Vafa mechanism for decompactification are pointed out. In both pure Einstein and dilaton gravities, we study cosmology of winding brane gases in a continuum approximation. The energy momentum tensor is obtained by coupling the brane action to the gravity action and we present several exact solutions for various brane configurations. T-duality invariance of the solutions are established in dilaton gravity. Our results indicate that phenomenologically the most viable scenario can be realized when there is only one brane wrapping over all extra dimensions.Comment: 17 pages, RevTex4, 2 figures, a paragraph added, to appear in Classical and Quantum Gravit

Regular S-Brane Backgrounds

We construct time-dependent S-brane solutions to the supergravity field equations in various dimensions which (unlike most such geometries) do not contain curvature singularities. The configurations we consider are less symmetric than are earlier solutions, with our simplest solution being obtained by a simple analytical continuation of the Kerr geometry. We discuss in detail the global structure and properties of this background. We then generalize it to higher dimensions and to include more complicated field configurations - like non vanishing scalars and antisymmetric tensor gauge potentials - by the usual artifice of applying duality symmetries.Comment: 22 pages, 3 figures. Typos in eq.(2.6) correcte

AdS3_3 vacua and RG flows in three dimensional gauged supergravities

We study $AdS_3$ supersymmetric vacua in N=4 and N=8, three dimensional gauged supergravities, with scalar manifolds $(\frac{SO(4,4)}{SO(4)\times SO(4)})^2$ and $\frac{SO(8,8)}{SO(8)\times SO(8)}$, non-semisimple Chern-Simons gaugings $SO(4)\ltimes {\bf R}^6$ and $(SO(4)\ltimes {\bf R}^6)^2$, respectively. These are in turn equivalent to SO(4) and $SO(4)\times SO(4)$ Yang-Mills theories coupled to supergravity. For the N=4 case, we study renormalization group flows between UV and IR $AdS_3$ vacua with the same amount of supersymmetry: in one case, with (3,1) supersymmetry, we can find an analytic solution whereas in another, with (2,0) supersymmetry, we give a numerical solution. In both cases, the flows turn out to be v.e.v. flows, i.e. they are driven by the expectation value of a relevant operator in the dual $SCFT_2$. These provide examples of v.e.v. flows between two $AdS_3$ vacua within a gauged supergravity framework.Comment: 35 pages in JHEP form, 3 figures, typos corrected, references adde

Hyperbolic Space Cosmologies

We present a systematic study of accelerating cosmologies obtained from M/string theory compactifications of hyperbolic spaces with time-varying volume. A set of vacuum solutions where the internal space is a product of hyperbolic manifolds is found to give qualitatively the same accelerating four-dimensional FLRW universe behavior as a single hyperbolic space. We also examine the possibility that our universe is a hyperbolic space and provide exact Milne type solutions, as well as intersecting S-brane solutions. When both the usual 4D spacetime and the m-dimensional internal space are hyperbolic, we find eternally accelerating cosmologies for $m\geq 7$, with and without form field backgrounds. In particular, the effective potential for a magnetic field background in the large 3 dimensions is positive definite with a local minimum and thus enhances the eternally accelerating expansion.Comment: 33 pages, 2 figures; v2 refs added; v3 minor change in text, JHEP versio

3D N=6 Gauged Supergravity: Admissible Gauge Groups, Vacua and RG Flows

We study N=6 gauged supergravity in three dimensions with scalar manifolds $\frac{SU(4,k)}{S(U(4)\times U(k))}$ for $k=1,2,3,4$ in great details. We classify some admissible non-compact gauge groups which can be consistently gauged and preserve all supersymmetries. We give the explicit form of the embedding tensors for these gauge groups as well as study their scalar potentials on the full scalar manifold for each value of $k=1,2,3,4$ along with the corresponding vacua. Furthermore, the potentials for the compact gauge groups, $SO(p)\times SO(6-p)\times SU(k)\times U(1)$ for $p=3,4,5,6$, identified previously in the literature are partially studied on a submanifold of the full scalar manifold. This submanifold is invariant under a certain subgroup of the corresponding gauge group. We find a number of supersymmetric AdS vacua in the case of compact gauge groups. We then consider holographic RG flow solutions in the compact gauge groups $SO(6)\times SU(4)\times U(1)$ and $SO(4)\times SO(2)\times SU(4)\times U(1)$ for the k=4 case. The solutions involving one active scalar can be found analytically and describe operator flows driven by a relevant operator of dimension 3/2. For non-compact gauge groups, we find all types of vacua namely AdS, Minkowski and dS, but there is no possibility of RG flows in the AdS/CFT sense for all gauge groups considered here.Comment: 43 pages, no figures references added, typoes corrected and more information adde

Particle Production on Half S-brane

In this paper we will study quantum field theory of fluctuation modes around the rolling tachyon solution on non-BPS D-brane effective action. The goal of this paper is to study particle production during the decay of non-BPS D-brane and explore possible relation with minisuperspace calculation. We find that the number of particles produced on half S-brane exponentially grows for large time which suggests that linearised approximation breaks down and also that backreaction of fluctuation field on classical solution should be taken into account.Comment: 24 pages,v1.references adde

The GS String Action on AdS(3)xS(3) with Ramond-Ramond Charge

We derive the classical kappa-symmetric Type IIB string action on AdS(3) x S(3) by employing the SU(1,1|2)^2 algebra. We then gauge fix kappa-symmetry in the background adapted Killing spinor gauge and present the action in a very simple form.Comment: 19 pages, LaTe