568 research outputs found
Deformations of Cosmological Solutions of D=11 Supergravity
We study Lunin-Maldacena deformations of cosmological backgrounds of D=11
supergravity which gives an easy way to generate solutions with nonzero 4-form
flux starting from solutions of pure Einstein equations which possess at least
three U(1) isometries. We illustrate this on the vacuum S-brane solution from
which the usual SM2-brane solution is obtained. Applying the method again, one
either gets the recently found S-brane system where contribution of the
Chern-Simons term to field equations is non-zero or the SM2-SM2(0)
intersection, depending on which U(1) directions are used during the process.
Repeated usage of the procedure gives rise to configurations with several
overlapping S-branes some of which are new. We also employ this method to
construct two more new solutions and make comments about accelerating
cosmologies that follow from such deformed solutions after compactification to
(1+3)-dimensions.Comment: v2:some comments and references adde
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
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
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
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
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
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
6D Dyonic String With Active Hyperscalars
We derive the necessary and sufficient conditions for the existence of a
Killing spinor in N=(1,0) gauge supergravity in six dimensions coupled to a
single tensor multiplet, vector multiplets and hypermultiplets. These are shown
to imply most of the field equations and the remaining ones are determined. In
this framework, we find a novel 1/8 supersymmetric dyonic string solution with
nonvanishing hypermultiplet scalars. The activated scalars parametrize a 4
dimensional submanifold of a quaternionic hyperbolic ball. We employ an
identity map between this submanifold and the internal space transverse to the
string worldsheet. The internal space forms a 4 dimensional analog of the
Gell-Mann-Zwiebach tear-drop which is noncompact with finite volume. While the
electric charge carried by the dyonic string is arbitrary, the magnetic charge
is fixed in Planckian units, and hence necessarily non-vanishing. The source
term needed to balance a delta function type singularity at the origin is
determined. The solution is also shown to have 1/4 supersymmetric AdS_3 x S^3
near horizon limit where the radii are proportional to the electric charge.Comment: 28 pages, latex, minor corrections mad
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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