582 research outputs found
Inflection Point Inflation and Time Dependent Potentials in String Theory
We consider models of inflection point inflation. The main drawback of such
models is that they suffer from the overshoot problem. Namely the initial
condition should be fine tuned to be near the inflection point for the universe
to inflate. We show that stringy realizations of inflection point inflation are
common and offer a natural resolution to the overshoot problem.Comment: 15 pages, 2 figures, refs. adde
Black Hole Information vs. Locality
We discuss the limitations on space time measurement in the Schwarzchild
metric. We find that near the horizon the limitations on space time measurement
are of the order of the black hole radius. We suggest that it indicates that a
large mass black hole cannot be described by means of local field theory even
at macroscopic distances and that any attempt to describe black hole formation
and evaporation by means of an effective local field theory will necessarily
lead to information loss. We also present a new interpretation of the black
hole entropy which leads to , where is a constant of order which
does not depend on the number of fields.Comment: 19 pages, final version to appear in Phys. Rev.
Holographic description of D3-branes in flat space
We describe a scheme for constructing the holographic dual of the full
D3-brane geometry with charge by embedding it into a large anti-de Sitter
space of size . Such a geometry is realized in a multi-center anti-de Sitter
geometry which admits a simple field theory interpretation as gauge
theory broken to . We find that the characteristic size of
the D3-brane geometry is of order where is the scale of
the Higgs. By choosing to be much larger than , the scale of the
D3-brane metric can be well separated from the Higgs scale in the radial
coordinate. We generalize the holographic energy-distance relation and estimate
the characteristic energy scale associated with these radial scales, and find
that the relation becomes effectively independent in the range
. This implies that all detailed structure of the
D3-brane geometry is encoded in the fine structure of the boundary gauge theory
at around the Higgs scale.Comment: 8 pages, 1 eps figur
On 't Hooft's S-matrix Ansatz for quantum black holes
The S-matrix Ansatz has been proposed by 't Hooft to overcome difficulties
and apparent contradictions of standard quantum field theory close to the black
hole horizon. In this paper we revisit and explore some of its aspects. We
start by computing gravitational backreaction effects on the properties of the
Hawking radiation and explain why a more powerful formalism is needed to encode
them. We then use the map bulk-boundary fields to investigate the nature of
exchange algebras satisfied by operators associated with ingoing and outgoing
matter. We propose and comment on some analogies between the non covariant form
of the S-matrix amplitude and liquid droplet physics to end up with
similarities with string theory amplitudes via an electrostatic analogy. We
finally recall the difficulties that one encounters when trying to incorporate
non linear gravity effects in 't Hooft's S-matrix and observe how the inclusion
of higher order derivatives might help in the black hole microstate counting.Comment: 22 Pages. Latex Fil
Dynamical Fine Tuning in Brane Inflation
We investigate a novel mechanism of dynamical tuning of a flat potential in
the open string landscape within the context of warped brane-antibrane
inflation in type IIB string theory. Because of competing effects between
interactions with the moduli stabilizing D7-branes in the warped throat and
anti-D3-branes at the tip, a stack of branes gives rise to a local minimum of
the potential, holding the branes high up in the throat. As branes successively
tunnel out of the local minimum to the bottom of the throat the potential
barrier becomes lower and is eventually replaced by a flat inflection point,
around which the remaining branes easily inflate. This dynamical flattening of
the inflaton potential reduces the need to fine tune the potential by hand, and
also leads to successful inflation for a larger range of inflaton initial
conditions, due to trapping in the local minimum.Comment: 23 pages, 9 figures. v2: Updated D3-dependence in potential, small
changes to numerical result
Fate of the Black String Instability
Gregory and Laflamme showed that certain nonextremal black strings (and
p-branes) are unstable to linearized perturbations. It is widely believed that
this instability will cause the black string horizon to classically pinch off
and then quantum mechanically separate, resulting in higher dimensional black
holes. We argue that this cannot happen. Under very mild assumptions, classical
event horizons cannot pinch off. Instead, they settle down to new static black
string solutions which are not translationally invariant along the string.Comment: 11 pages, v2: few clarifications and references adde
Ten Dimensional Black Hole and the D0-brane Threshold Bound State
We discuss the ten dimensional black holes made of D0-branes in the regime
where the effective coupling is large, and yet the 11D geometry is unimportant.
We suggest that these black holes can be interpreted as excitations over the
threshold bound state. Thus, the entropy formula for the former is used to
predict a scaling region of the wave function of the latter. The horizon radius
and the mass gap predicted in this picture agree with the formulas derived from
the classical geometry.Comment: 11 pages, harvmac; v2: typos corrected, argument for the convergence
of two integrals improved, v3: one ref. adde
D-Sitter Space: Causal Structure, Thermodynamics, and Entropy
We study the entropy of concrete de Sitter flux compactifications and
deformations of them containing D-brane domain walls. We determine the relevant
causal and thermodynamic properties of these "D-Sitter" deformations of de
Sitter spacetimes. We find a string scale correspondence point at which the
entropy localized on the D-branes (and measured by probes sent from an observer
in the middle of the bubble) scales the same with large flux quantum numbers as
the entropy of the original de Sitter space, and at which Bousso's bound is
saturated by the D-brane degrees of freedom (up to order one coefficients) for
an infinite range of times. From the geometry of a static patch of D-Sitter
space and from basic relations in flux compactifications, we find support for
the possibility of a low energy open string description of the static patch of
de Sitter space.Comment: 46 pages, harvmac big; 14 figure
Towards the Final Fate of an Unstable Black String
Black strings, one class of higher dimensional analogues of black holes, were
shown to be unstable to long wavelength perturbations by Gregory and Laflamme
in 1992, via a linear analysis. We revisit the problem through numerical
solution of the full equations of motion, and focus on trying to determine the
end-state of a perturbed, unstable black string. Our preliminary results show
that such a spacetime tends towards a solution resembling a sequence of
spherical black holes connected by thin black strings, at least at intermediate
times. However, our code fails then, primarily due to large gradients that
develop in metric functions, as the coordinate system we use is not well
adapted to the nature of the unfolding solution. We are thus unable to
determine how close the solution we see is to the final end-state, though we do
observe rich dynamical behavior of the system in the intermediate stages.Comment: 17 pages, 7 figure
On Minimal N=4 Topological Strings And The (1,k) Minimal Bosonic String
In this paper we consider tree-level scattering in the minimal N=4
topological string and show that a large class of N-point functions can be
recast in terms of corresponding amplitudes in the (1,k) minimal bosonic
string. This suggests a non-trivial relation between the minimal N=4
topological strings, the (1,k) minimal bosonic strings and their corresponding
ADE matrix models. This relation has interesting and far-reaching implications
for the topological sector of six-dimensional Little String Theories.Comment: lanlmac, 30 pages; v3 minor revisions, version published in JHE
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