234 research outputs found
Supersymmetric Strings and Waves in D=3, N=2 Matter Coupled Gauged Supergravities
We construct new 1/2 supersymmetric solutions in D=3, N=2, matter coupled,
U(1) gauged supergravities and study some of their properties. In the most
general case they represent a string superposed with gravitational and
Chern-Simons electromagnetic waves. The waves are attached to the string and
the solution satisfies an electromagnetic self-duality relation. When the sigma
model is non-compact it interpolates between an asymptotically Kaigorodov space
and a naked singularity. For the compact sigma model there is a regular horizon
with the Kaigorodov geometry and asymptotically it is either Minkowskian or a
pp-wave. When the sigma manifold is flat our solutions describe either AdS_3 or
Kaigorodov space or a pp-wave in AdS_3.Comment: 19 pages, 1 figure, v2:a reference added, minor improvement
AdS/CFT and Randall-Sundrum Model Without a Brane
We reformulate the Randall-Sundrum (RS) model on the compactified AdS by
adding a term proportional to the area of the boundary to the usual gravity
action with a negative cosmological constant and show that gravity can still be
localized on the boundary without introducing singular brane sources. The
boundary conditions now follow from the field equations, which are obtained by
letting the induced metric vary on the boundary. This approach gives similar
modes that are obtained in [1] and clarifies the complementarity of the RS and
the AdS/CFT pictures. Normalizability of these modes is checked by an
inner-product in the space of linearized perturbations. The same conclusions
hold for a massless scalar field in the bulk.Comment: Comments and references added, to apear in JHE
A Note on Supergravity Solutions for Partially Localized Intersecting Branes
Using the method developed by Cherkis and Hashimoto we construct partially
localized D3/D5(2), D4/D4(2) and M5/M5(3) supergravity solutions where one of
the harmonic functions is given in an integral form. This is a generalization
of the already known near-horizon solutions. The method fails for certain
intersections such as D1/D5(1) which is consistent with the previous no-go
theorems. We point out some possible ways of bypassing these results.Comment: 9 pages, 2 figures, revtex
Calibrated Entanglement Entropy
The Ryu-Takayanagi prescription reduces the problem of calculating
entanglement entropy in CFTs to the determination of minimal surfaces in a dual
anti-de Sitter geometry. For 3D gravity theories and BTZ black holes, we
identify the minimal surfaces as special Lagrangian cycles calibrated by the
real part of the holomorphic one-form of a spacelike hypersurface. We show that
(generalised) calibrations provide a unified way to determine holographic
entanglement entropy from minimal surfaces, which is applicable to warped
AdS geometries. We briefly discuss generalisations to higher dimensions.Comment: v1 22 pages, 1 figure; v2 appendix improved and moved into the body
to show the application of calibrations to find minimal surfaces in warped
AdS, matches published versio
The Third Way to Interacting p-form Theories
We construct a class of interacting -form theories in dimensions that are `third way' consistent. This refers to the fact that the interaction terms in the -form field equations of motion neither come from the variation of an action nor are they off-shell conserved on their own. Nevertheless the full equation is still on-shell consistent. Various generalizations, e.g. coupling them to -forms, where 3-algebras play a prominent role, are also discussed. The method to construct these models also easily recovers the modified 3 Yang-Mills theory obtained earlier and straightforwardly allows for higher derivative extensions
Accelerating Cosmologies from S-Branes
We point out that the recently proposed model of a flat 4-dimensional
universe with accelerated expansion in string/M-theory is a special case of
time-dependent solutions that the author found under the name of ``S-branes.''
We also show that similar accelerating models can be obtained from S-branes if
the internal space is chosen to be hyperbolic or flat spaces.Comment: 8 pages, 4 figures, comments added, a typo corrected, final version
to appear in Phys. Rev. Let
A note on accelerating cosmologies from compactifications and S-branes
We give a simple interpretation of the recent solutions for cosmologies with
a transient accelerating phase obtained from compactification in hyperbolic
manifolds, or from S-brane solutions of string/M-theory. In the
four-dimensional picture, these solutions correspond to bouncing the radion
field off its exponential potential. Acceleration occurs at the turning point,
when the radion stops and the potential energy momentarily dominates. The
virtues and limitations of these approaches become quite transparent in this
interpretation.Comment: 9 pages, 1 figure. References 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
Anti-de-Sitter Island-Universes from 5D Standing Waves
We construct simple standing wave solutions in a 5D space-time with a ghost
scalar field. The nodes of these standing waves are 'islands' of 4D Minkowski
space-time. For the 5D model with increasing (decreasing) warp factor there are
a finite (infinite) number of nodes and thus Minkowski island-universes having
different parameters, such as gravitational and cosmological constants. This
feature is similar to the assumptions of the landscape models, which postulate
a large number of universes with different parameters. This standing wave
solution also provides a new localization mechanism - matter fields can reside
only on Minkowski 'islands', where the background space-time does not
oscillate.Comment: 14 page pre-print format. Discussion about connection to Weyl gravity
added and "E&M" localization method added. To be published MPL
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