512 research outputs found
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
(2,0) Chern-Simons Supergravity Plus Matter Near the Boundary of AdS_3
We examine the boundary behaviour of the gauged N=(2,0) supergravity in D=3
coupled to an arbitrary number of scalar supermultiplets which parametrize a
Kahler manifold. In addition to the gravitational coupling constant, the model
depends on two parameters, namely the cosmological constant and the size of the
Kahler manifold. It is shown that regular and irregular boundary conditions can
be imposed on the matter fields depending on the size of the sigma model
manifold. It is also shown that the super AdS transformations in the bulk
produce the transformations of the N=(2,0) conformal supergravity and scalar
multiplets on the boundary, containing fields with nonvanishing Weyl weights
determined by the ratio of the sigma model and the gravitational coupling
constants. Various types of (2,0) superconformal multiplets are found on the
boundary and in one case the superconformal symmetry is shown to be realized in
an unconventional way.Comment: 28 pages, latex, references adde
Matter Coupled AdS_3 Supergravities and Their Black Strings
We couple n copies of N=(2,0) scalar multiplets to a gauged N=(2,0)
supergravity in 2+1 dimensions which admits AdS_3 as a vacuum. The scalar
fields are charged under the gauged R-symmetry group U(1) and parametrize
certain Kahler manifolds with compact or non-compact isometries. The radii of
these manifolds are quantized in the compact case, but arbitrary otherwise. In
the compact case, we find half-supersymmetry preserving and asymptotically
Minkowskian black string solutions. For a particular value of the scalar
manifold radius, the solution coincides with that of Horne and Horowitz found
in the context of a string theory in 2+1 dimensions. In the non-compact case,
we find half-supersymmetry preserving and asymptotically AdS_3 string solutions
which have naked singularities. We also obtain two distinct AdS_3
supergravities coupled to n copies of N=(1,0) scalar multiplets either by the
truncation of the (2,0) model or by a direct construction.Comment: 20 pages, latex, typos corrected in Sec.
Comments on Supergravity Description of S-branes
This is a note on the coupled supergravity-tachyon matter system, which has
been earlier proposed as a candidate for the effective space-time description
of S-branes. In particular, we study an ansatz with the maximal
ISO(p+1)xSO(8-p,1) symmetry, for general brane dimensionality p and homogeneous
brane distribution in transverse space \rho_\perp. A simple application of
singularity theorems shows that (for p \le 7) the most general solution with
these symmetries is always singular. (This invalidates a recent claim in the
literature.) We include a few general comments about the possibility of
describing the decay of unstable D-branes in purely gravitational terms.Comment: 19 pages, refs adde
Chern-Simons S-Brane Solutions in M-theory and Accelerating Cosmologies
We construct an intersecting S-brane solution of 11-dimensional supergravity
for which the contribution of the Chern-Simons term to the field equations is
non-zero. After studying some of its properties, we consider three different
compactifications (each with 3 separate subcases) of this system to
4-dimensions. Two of these give accelerating cosmologies, however their
expansion factors are of order unity. We also find two static versions of this
configuration and its dimensional reduction to type IIA theory.Comment: 18 pages, v3: a new static solution and references added, v4:
references added, to appear in JHE
Supergravity Solutions for Harmonic, Static and Flux S-Branes
We seek S-brane solutions in D=11 supergravity which can be characterized by
a harmonic function H on the flat transverse space. It turns out that the
Einstein's equations force H to be a linear function of the transverse
coordinates. The codimension one H=0 hyperplane can be spacelike, timelike or
null and the spacelike case reduces to the previously obtained SM2 or SM5 brane
solutions. We then consider static S-brane configurations having smeared
timelike directions where the transverse Lorentzian symmetry group is broken
down to its maximal orthogonal subgroup. Assuming that the metric functions
depend on a radial spatial coordinate, we construct explicit solutions in D=11
supergravity which are non-supersymmetric and asymptotically flat. Finally, we
obtain spacelike fluxbrane backgrounds which have timelike electric or magnetic
fluxlines extending from past to future infinity.Comment: 22 pages, v2: references adde
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
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
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