250 research outputs found
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
AdS vacua and RG flows in three dimensional gauged supergravities
We study supersymmetric vacua in N=4 and N=8, three dimensional
gauged supergravities, with scalar manifolds and , non-semisimple Chern-Simons
gaugings and ,
respectively. These are in turn equivalent to SO(4) and
Yang-Mills theories coupled to supergravity. For the N=4 case, we study
renormalization group flows between UV and IR 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
. These provide examples of v.e.v. flows between two 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 , 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
for 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 along with
the corresponding vacua. Furthermore, the potentials for the compact gauge
groups, for ,
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 and
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
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