6,164 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
A New Handle on de Sitter Compactifications
We construct a large new class of de Sitter (and anti de Sitter) vacua of
critical string theory from flux compactifications on products of Riemann
surfaces. In the construction, the leading effects stabilizing the moduli are
perturbative. We show that these effects self-consistently dominate over
standard estimates for further and quantum corrections, via
tuning available from large flux and brane quantum numbers.Comment: 26 pages, harvmac big. v2: Correction generalizing specific
ingredients required for tunable negative term; conclusions and structure of
potential unchange
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
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
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
Fine tuning and the ratio of tensor to scalar density fluctuations from cosmological inflation
The form of the inflationary potential is severely restricted if one requires
that it be natural in the technical sense, i.e. terms of unrelated origin are
not required to be correlated. We determine the constraints on observables that
are implied in such natural inflationary models, in particular on , the
ratio of tensor to scalar perturbations. We find that the naturalness
constraint does not require to be lare enough to be detectable by the
forthcoming searches for B-mode polarisation in CMB maps. We show also that the
value of is a sensitive discriminator between inflationary models.Comment: 8 pages LaTeX; clarifications and a reference added; to appear in
JCA
Fibrin regulates neutrophil migration in response to interleukin 8, leukotriene B4, tumor necrosis factor, and formyl-methionyl-leucyl-phenylalanine
We have examined the capacity of four different chemoattractants/cytokines to promote directed migration of polymorphonuclear leukocytes (PMN) through three-dimensional gels composed of extracellular matrix proteins. About 20% of PMN migrated through fibrin gels and plasma clots in response to a gradient of interleukin 8 (IL-8) or leukotriene B4 (LTB4). In contrast, < 0.3% of PMN migrated through fibrin gels in response to a gradient of tumor necrosis factor alpha (TNF) or formyl-methionyl-leucyl-phenylalanine (FMLP). All four chemoattractants stimulated PMN to migrate through gels composed of collagen IV or of basement membrane proteins (Matrigel), or through filters to which fibronectin or fibrinogen had been adsorbed. PMN stimulated with TNF or FMLP adhered and formed zones of close apposition to fibrin, as measured by the exclusion of a 10-kD rhodamine-polyethylene glycol probe from the contact zones between PMN and the underlying fibrin gel. By this measure, IL-8- or LTB4-treated PMN adhered loosely to fibrin, since 10 kD rhodamine-polyethylene glycol permeated into the contact zones between these cells and the underlying fibrin gel. PMN stimulated with FMLP and IL-8, or FMLP and LTB4, exhibited very little migration through fibrin gels, and three times as many of these cells excluded 10 kD rhodamine-polyethylene glycol from their zones of contact with fibrin as PMN stimulated with IL-8 or LTB4 alone. These results show that PMN chemotaxis is regulated by both the nature of the chemoattractant and the composition of the extracellular matrix; they suggest that certain combinations of chemoattractants and matrix proteins may limit leukocyte movements and promote their localization in specific tissues in vivo
Closed string tachyons, flips and conifolds
Following the analysis of tachyons and orbifold flips described in
hep-th/0412337, we study nonsupersymmetric analogs of the supersymmetric
conifold singularity and show using their toric geometry description that they
are nonsupersymmetric orbifolds of the latter. Using linear sigma models, we
see that these are unstable to localized closed string tachyon condensation and
exhibit flip transitions between their two small resolutions (involving
2-cycles), in the process mediating mild dynamical topology change. Our
analysis shows that the structure of these nonsupersymmetric conifolds as
quotients of the supersymmetric conifold obstructs the 3-cycle deformation of
such singularities, suggesting that these nonsupersymmetric conifolds decay by
evolving towards their stable small resolutions.Comment: Latex, 22 pgs, 2 figs. v4: matches JHEP version, 29 pgs, 3 figures,
more elaborate Introduction, various clarifications adde
Negotiations of minority ethnic rugby league players in the Cathar country of France
This article is based on new empirical, qualitative research with minority ethnic rugby league players in the southwest of France. Drawing on similar research on rugby league in the north and the south of England, the article examines how rugby league, traditionally viewed as a white, working-class male game (Collins, 2006; Denham, 2004; Spracklen, 1995, 2001) has had to re-imagine its symbolic boundaries as they are constituted globally and locally to accommodate the needs of players from minority ethnic backgrounds. In particular, the article examines the sense in which experiences of minority ethnic rugby league players in France compare with those of their counterparts in England (Spracklen, 2001, 2007), how rugby league is used in France to construct identity, and in what sense the norms associated with the imaginary community of rugby league are replicated or challenged by the involvement of minority ethnic rugby league players in France. Questions about what it means to be (provincial, national) French (Kumar, 2006) are posed, questions that relate to the role of sport in the construction of Frenchness, and in particular the role of rugby league (and union). © Copyright ISSA and SAGE Publications
- âŠ