53 research outputs found
Coleman meets Schwinger
It is well known that spherical D-branes are nucleated in the presence of an
external RR electric field. Using the description of D-branes as solitons of
the tachyon field on non-BPS D-branes, we show that the brane nucleation
process can be seen as the decay of the tachyon false vacuum. This process can
describe the decay of flux-branes in string theory or the decay of quintessence
potentials arising in flux compactifications.Comment: 5 pages, 2 figure
Diffractive Higgs Production by AdS Pomeron Fusion
The double diffractive Higgs production at central rapidity is formulated in
terms of the fusion of two AdS gravitons/Pomerons first introduced by Brower,
Polchinski, Strassler and Tan in elastic scattering. Here we propose a simple
self-consistent holographic framework capable of providing phenomenologically
compelling estimates of diffractive cross sections at the LHC. As in the
traditional weak coupling approach, we anticipate that several phenomenological
parameters must be tested and calibrated through factorization for a
self-consistent description of other diffractive process such as total cross
sections, deep inelastic scattering and heavy quark production in the central
region.Comment: 53 pages, 8 figure
On the Classical Stability of Orientifold Cosmologies
We analyze the classical stability of string cosmologies driven by the
dynamics of orientifold planes. These models are related to time-dependent
orbifolds, and resolve the orbifold singularities which are otherwise
problematic by introducing orientifold planes. In particular, we show that the
instability discussed by Horowitz and Polchinski for pure orbifold models is
resolved by the presence of the orientifolds. Moreover, we discuss the issue of
stability of the cosmological Cauchy horizon, and we show that it is stable to
small perturbations due to in-falling matter.Comment: 40 pages, 13 figures. Reference and conclusion added. Published
versio
The Kahler Cone as Cosmic Censor
M-theory effects prevent five-dimensional domain-wall and black-hole
solutions from developing curvature singularities. While so far this analysis
was performed for particular models, we now present a model-independent proof
that these solutions do not have naked singularities as long as the Kahler
moduli take values inside the extended Kahler cone. As a by-product we obtain
information on the regularity of the Kahler-cone metric at boundaries of the
Kahler cone and derive relations between the geometry of moduli space and
space-time.Comment: 21 pages, 1 figure. Improved discussion of the relation between
Kahler moduli and five-dimensional scalars. No changes in the conclusion
Clean Time-Dependent String Backgrounds from Bubble Baths
We consider the set of controlled time-dependent backgrounds of general
relativity and string theory describing ``bubbles of nothing'', obtained via
double analytic continuation of black hole solutions. We analyze their quantum
stability, uncover some novel features of their dynamics, identify their causal
structure and observables, and compute their particle production spectrum. We
present a general relation between squeezed states, such as those arising in
cosmological particle creation, and nonlocal theories on the string worldsheet.
The bubble backgrounds have various aspects in common with de Sitter space,
Rindler space, and moving mirror systems, but constitute controlled solutions
of general relativity and string theory with no external forces. They provide a
useful theoretical laboratory for studying issues of observables in systems
with cosmological horizons, particle creation, and time-dependent string
perturbation theory.Comment: 38 pages, harvmac big, 6 figure
Accelerating Cosmologies from Exponential Potentials
An exponential potential of the form arising from
the hyperbolic or flux compactification of higher-dimensional theories is of
interest for getting short periods of accelerated cosmological expansions.
Using a similar potential but derived for the combined case of hyperbolic-flux
compactification, we study the four-dimensional flat (and open) FLRW
cosmologies and give analytic (and numerical) solutions with exponential
behavior of scale factors. We show that, for the M-theory motivated potentials,
the cosmic acceleration of the universe can be eternal if the spatial curvature
of the 4d spacetime is negative, while the acceleration is only transient for a
spatially flat universe. We also comment on the size of the internal space and
its associated geometric bounds on massive Kaluza-Klein excitations.Comment: 17 pages, 6 figures; minor typos fixe
Quotients of AdS_{p+1} x S^q: causally well-behaved spaces and black holes
Starting from the recent classification of quotients of Freund--Rubin
backgrounds in string theory of the type AdS_{p+1} x S^q by one-parameter
subgroups of isometries, we investigate the physical interpretation of the
associated quotients by discrete cyclic subgroups. We establish which quotients
have well-behaved causal structures, and of those containing closed timelike
curves, which have interpretations as black holes. We explain the relation to
previous investigations of quotients of asymptotically flat spacetimes and
plane waves, of black holes in AdS and of Godel-type universes.Comment: 48 pages; v2: minor typos correcte
Spinning Conformal Correlators
We develop the embedding formalism for conformal field theories, aimed at
doing computations with symmetric traceless operators of arbitrary spin. We use
an index-free notation where tensors are encoded by polynomials in auxiliary
polarization vectors. The efficiency of the formalism is demonstrated by
computing the tensor structures allowed in n-point conformal correlation
functions of tensors operators. Constraints due to tensor conservation also
take a simple form in this formalism. Finally, we obtain a perfect match
between the number of independent tensor structures of conformal correlators in
d dimensions and the number of independent structures in scattering amplitudes
of spinning particles in (d+1)-dimensional Minkowski space.Comment: 46 pages, 3 figures; V2: references added; V3: tiny misprint
corrected in (A.9
Open Strings in Exactly Solvable Model of Curved Spacetime and PP-Wave Limit
In this paper we study the superstring version of the exactly solvable string
model constructed by Russo and Tseytlin. This model represents superstring
theory in a curved spacetime and can be seen as a generalization of the Melvin
background. We investigate D-branes in this model as probes of the background
geometry by constructing the boundary states. We find that spacetime
singularities in the model become smooth at high energy from the viewpoint of
open string. We show that there always exist bulk (movable) D-branes by the
effect of electric flux. The model also includes Nappi-Witten model as the
Penrose limit and supersymmetry is enhanced in the limit. We examine this
phenomenon in the open string spectrum. We also find the similar enhancement of
supersymmetry can be occurred in several coset models.Comment: Latex, 32 pages, typos corrected, references added, to appear in
JHEP, eq.(2.22) correcte
AdS Field Theory from Conformal Field Theory
We provide necessary and sufficient conditions for a Conformal Field Theory
to have a description in terms of a perturbative Effective Field Theory in AdS.
The first two conditions are well-known: the existence of a perturbative `1/N'
expansion and an approximate Fock space of states generated by a finite number
of low-dimension operators. We add a third condition, that the Mellin
amplitudes of the CFT correlators must be well-approximated by functions that
are bounded by a polynomial at infinity in Mellin space, or in other words,
that the Mellin amplitudes have an effective theory-type expansion. We explain
the relationship between our conditions and unitarity, and provide an analogy
with scattering amplitudes that becomes exact in the flat space limit of AdS.
The analysis also yields a simple connection between conformal blocks and AdS
diagrams, providing a new calculational tool very much in the spirit of the
S-Matrix program.
We also begin to explore the potential pathologies associated with higher
spin fields in AdS by generalizing Weinberg's soft theorems to AdS/CFT. The AdS
analog of Weinberg's argument constrains the interactions of conserved currents
in CFTs, but there are potential loopholes that are unavailable to theories of
massless higher spin particles in flat spacetime.Comment: 31+7 pages, 5 figure
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