124 research outputs found
Dielectric (p,q) Strings in a Throat
We calculate the (p,q) string spectrum in a warped deformed conifold using
the dielectric brane method. The spectrum is shown to have the same functional
form as in the dual picture of a wrapped D3-brane with electric and magnetic
fluxes on its world volume. The agreement is exact in the limit where q is
large. We also calculate the dielectric spectrum in the S-dual picture. The
spectrum in the S-dual picture has the same form as in the original picture but
it is not exactly S-dual invariant due to an interchange of Casimirs of the
non-Abelian gauge symmetries. We argue that in order to restore S-duality
invariance the non-Abelian brane action should be refined, probably by a better
prescription for the non-Abelian trace operation
Superstars and Giant Gravitons in M-theory
Following hep-th/0109127, we show that a certain class of BPS naked
singularities (superstars) found in compactifications of M-theory can be
interpreted as being composed of giant gravitons. More specifically, we study
superstars which are asymptotically AdS_7 x S^4 and AdS_4 x S^7 and show that
these field configurations can be interpreted as being sourced by continuous
distributions of spherical M2- and M5-branes, respectively, which carry
internal momenta and have expanded on the spherical component of the
space-time.Comment: 13 page
The (p,q) String Tension in a Warped Deformed Conifold
We find the tension spectrum of the bound states of p fundamental strings and
q D-strings at the bottom of a warped deformed conifold. We show that it can be
obtained from a D3-brane wrapping a 2-cycle that is stabilized by both electric
and magnetic fluxes. Because the F-strings are Z_M-charged with non-zero
binding energy, binding can take place even if (p,q) are not coprime.
Implications for cosmic strings are briefly discussed.Comment: 17 pages, 1 figur
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
An Inflationary Scenario in Intersecting Brane Models
We propose a new scenario for D-term inflation which appears quite
straightforwardly in the open string sector of intersecting brane models. We
take the inflaton to be a chiral field in a bifundamental representation of the
hidden sector and we argue that a sufficiently flat potential can be brane
engineered. This type of model generically predicts a near gaussian red
spectrum with negligible tensor modes. We note that this model can very
naturally generate a baryon asymmetry at the end of inflation via the recently
proposed hidden sector baryogenesis mechanism. We also discuss the possibility
that Majorana masses for the neutrinos can be simultaneously generated by the
tachyon condensation which ends inflation. Our proposed scenario is viable for
both high and low scale supersymmetry breaking.Comment: 30 pages, 2 figures; v2 references and comments adde
The Shape of Gravity in a Warped Deformed Conifold
We study the spectrum of the gravitational modes in Minkowski spacetime due
to a 6-dimensional warped deformed conifold, i.e., a warped throat, in
superstring theory. After identifying the zero mode as the usual 4D graviton,
we present the KK spectrum as well as other excitation modes. Gluing the throat
to the bulk (a realistic scenario), we see that the graviton has a rather
uniform probability distribution everywhere while a KK mode is peaked in the
throat, as expected. Due to the suppressed measure of the throat in the wave
function normalization, we find that a KK mode's probability in the bulk can be
comparable to that of the graviton mode. We also present the tunneling
probabilities of a KK mode from the inflationary throat to the bulk and to
another throat. Due to resonance effect, the latter may not be suppressed as
natively expected. Implication of this property to reheating after brane
inflation is discussed
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
The Strong Energy Condition and the S-Brane Singularity Problem
Recently it has been argued that, because tachyonic matter satisfies the
Strong Energy Condition [SEC], there is little hope of avoiding the
singularities which plague S-Brane spacetimes. Meanwhile, however, Townsend and
Wohlfarth have suggested an ingenious way of circumventing the SEC in such
situations, and other suggestions for actually violating it in the S-Brane
context have recently been proposed. Of course, the natural context for
discussions of [effective or actual] violations of the SEC is the theory of
asymptotically deSitter spacetimes, which tend to be less singular than
ordinary FRW spacetimes. However, while violating or circumventing the SEC is
necessary if singularities are to be avoided, it is not at all clear that it is
sufficient. That is, we can ask: would an asymptotically deSitter S-brane
spacetime be non-singular? We show that this is difficult to achieve; this
result is in the spirit of the recently proved "S-brane singularity theorem".
Essentially our results suggest that circumventing or violating the SEC may not
suffice to solve the S-Brane singularity problem, though we do propose two ways
of avoiding this conclusion.Comment: 13 pages, minor corrections and improvements, references adde
Inflation from Warped Space
A long period of inflation can be triggered when the inflaton is held up on
the top of a steep potential by the infrared end of a warped space. We first
study the field theory description of such a model. We then embed it in the
flux stabilized string compactification. Some special effects in the throat
reheating process by relativistic branes are discussed. We put all these
ingredients into a multi-throat brane inflationary scenario. The resulting
cosmic string tension and a multi-throat slow-roll model are also discussed.Comment: 39 pages; v4, added reference, to appear in JHE
Breakdown of Semiclassical Methods in de Sitter Space
Massless interacting scalar fields in de Sitter space have long been known to
experience large fluctuations over length scales larger than Hubble distances.
A similar situation arises in condensed matter physics in the vicinity of a
critical point, and in this better-understood situation these large
fluctuations indicate the failure in this regime of mean-field methods. We
argue that for non-Goldstone scalars in de Sitter space, these fluctuations can
also be interpreted as signaling the complete breakdown of the semi-classical
methods widely used throughout cosmology. By power-counting the infrared
properties of Feynman graphs in de Sitter space we find that for a massive
scalar interacting through a \lambda \phi^4$ interaction, control over the loop
approximation is lost for masses smaller than m \simeq \sqrt \lambda H/2\pi,
where H is the Hubble scale. We briefly discuss some potential implications for
inflationary cosmology.Comment: 24 pages, 7 figures, v2; added references, clarified the resummation
discussio
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