6,861 research outputs found
AdS Bubbles, Entropy and Closed String Tachyons
We study the conjectured connection between AdS bubbles (AdS solitons) and
closed string tachyon condensations. We confirm that the entanglement entropy,
which measures the degree of freedom, decreases under the tachyon condensation.
The entropies in supergravity and free Yang-Mills agree with each other
remarkably. Next we consider the tachyon condensation on the AdS twisted circle
and argue that its endpoint is given by the twisted AdS bubble, defined by the
double Wick rotation of rotating black 3-brane solutions. We calculated the
Casimir energy and entropy and checked the agreements between the gauge and
gravity results. Finally we show an infinite boost of a null linear dilaton
theory with a tachyon wall (or bubble), leads to a solvable time-dependent
background with a bulk tachyon condensation. This is the simplest example of
spacetimes with null boundaries in string theory.Comment: 45 pages, 6 figures, harvmac, eq.(2.16) corrected, references adde
On the Matrix Description of Calabi-Yau Compactifications
We point out that the matrix description of M-theory compactified on
Calabi-Yau threefolds is in many respects simpler than the matrix description
of a compactification. This is largely because of the differences between
D6 branes wrapped on Calabi-Yau threefolds and D6 branes wrapped on six-tori.
In particular, if we define the matrix theory following the prescription of Sen
and Seiberg, we find that the remaining degrees of freedom are decoupled from
gravity.Comment: 12 pages, harvmac big; comment on 4d N=1 theories change
On the harmonic measure of stable processes
Using three hypergeometric identities, we evaluate the harmonic measure of a
finite interval and of its complementary for a strictly stable real L{\'e}vy
process. This gives a simple and unified proof of several results in the
literature, old and recent. We also provide a full description of the
corresponding Green functions. As a by-product, we compute the hitting
probabilities of points and describe the non-negative harmonic functions for
the stable process killed outside a finite interval
A Phase Transition between Small and Large Field Models of Inflation
We show that models of inflection point inflation exhibit a phase transition
from a region in parameter space where they are of large field type to a region
where they are of small field type. The phase transition is between a universal
behavior, with respect to the initial condition, at the large field region and
non-universal behavior at the small field region. The order parameter is the
number of e-foldings. We find integer critical exponents at the transition
between the two phases.Comment: 21 pages, 8 figure
Adventures in Holographic Dimer Models
We abstract the essential features of holographic dimer models, and develop
several new applications of these models. First, semi-holographically coupling
free band fermions to holographic dimers, we uncover novel phase transitions
between conventional Fermi liquids and non-Fermi liquids, accompanied by a
change in the structure of the Fermi surface. Second, we make dimer vibrations
propagate through the whole crystal by way of double trace deformations,
obtaining nontrivial band structure. In a simple toy model, the topology of the
band structure experiences an interesting reorganization as we vary the
strength of the double trace deformations. Finally, we develop tools that would
allow one to build, in a bottom-up fashion, a holographic avatar of the Hubbard
model.Comment: 22 pages, 8 figures; v2: brief description of case of pure D5 lattice
added in sec.3; v3: minor typo fixed; v4: minor change
Moduli Stabilization with Long Winding Strings
Stabilizing all of the modulus fields coming from compactifications of string
theory on internal manifolds is one of the outstanding challenges for string
cosmology. Here, in a simple example of toroidal compactification, we study the
dynamics of the moduli fields corresponding to the size and shape of the torus
along with the ambient flux and long strings winding both internal directions.
It is known that a string gas containing states with non-vanishing winding and
momentum number in one internal direction can stabilize the radius of this
internal circle to be at self-dual radius. We show that a gas of long strings
winding all internal directions can stabilize all moduli, except the dilaton
which is stabilized by hand, in this simple example.Comment: title changed, improved presentation; reference added. 18 pages, JHEP
styl
Beauty is Attractive: Moduli Trapping at Enhanced Symmetry Points
We study quantum effects on moduli dynamics arising from the production of
particles which are light at special points in moduli space. The resulting
forces trap the moduli at these points, which often exhibit enhanced symmetry.
Moduli trapping occurs in time-dependent quantum field theory, as well as in
systems of moving D-branes, where it leads the branes to combine into stacks.
Trapping also occurs in an expanding universe, though the range over which the
moduli can roll is limited by Hubble friction. We observe that a scalar field
trapped on a steep potential can induce a stage of acceleration of the
universe, which we call trapped inflation. Moduli trapping ameliorates the
cosmological moduli problem and may affect vacuum selection. In particular,
rolling moduli are most powerfully attracted to the points with the largest
number of light particles, which are often the points of greatest symmetry.
Given suitable assumptions about the dynamics of the very early universe, this
effect might help to explain why among the plethora of possible vacuum states
of string theory, we appear to live in one with a large number of light
particles and (spontaneously broken) symmetries. In other words, some of the
surprising properties of our world might arise not through pure chance or
miraculous cancellations, but through a natural selection mechanism during
dynamical evolution.Comment: 50 pages, 4 figures; v2: added references and an appendix describing
a related classical proces
Packing and Hausdorff measures of stable trees
In this paper we discuss Hausdorff and packing measures of random continuous
trees called stable trees. Stable trees form a specific class of L\'evy trees
(introduced by Le Gall and Le Jan in 1998) that contains Aldous's continuum
random tree (1991) which corresponds to the Brownian case. We provide results
for the whole stable trees and for their level sets that are the sets of points
situated at a given distance from the root. We first show that there is no
exact packing measure for levels sets. We also prove that non-Brownian stable
trees and their level sets have no exact Hausdorff measure with regularly
varying gauge function, which continues previous results from a joint work with
J-F Le Gall (2006).Comment: 40 page
Vortical Patterns in the Wake of an Oscillating Airfoil
The vortical flow patterns in the wake of a NACA 0012 airfoil pitching at small amplitudes are studied in a low speed water channel. it is shown that a great deal of control can be exercised on the structure of the wake by the control of the frequency, amplitude and also the shape of the oscillation waveform. An important observation in this study has been the existence of an axial flow along the cores of the wake vortices. Estimates of the magnitude of the axial flow suggest a linear dependence on the oscillation frequency and amplitude
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