181 research outputs found
Comment on Counting Black Hole Microstates Using String Dualities
We discuss a previous attempt at a microscopic counting of the entropy of
asymptotically flat non-extremal black-holes. This method used string dualities
to relate 4 and 5 dimensional black holes to the BTZ black hole. We show how
the dualities can be justified in a certain limit, equivalent to a near horizon
limit, but the resulting spacetime is no longer asymptotically flat.Comment: 10 pages, harvmac. v(2) typo correcte
A Note on Mirror Symmetry for Manifolds with Spin(7) Holonomy
Starting from the superconformal algebras associated with manifolds, I
extend the algebra to the manifolds with spin(7) holonomy. I show how the
mirror symmetry in manifolds with spin(7) holonomy arises as the automorphism
in the extended sperconformal algebra. The automorphism is realized as 14 kinds
of T-dualities on the supersymmetric toroidal fibrations. One class of
Joyce's orbifolds are pairwise identified under the symmetry.Comment: 12 pages, harvmac bi
On Witten's Instability and Winding Tachyons
We investigate, from a spacetime perspective, some aspects of Horowitz's
recent conjecture that black strings may catalyze the decay of Kaluza-Klein
spacetimes into a bubble of nothing. We identify classical configurations that
interpolate between flat space and the bubble, and discuss the energetics of
the transition. We investigate the effects of winding tachyons on the size and
shape of the barrier and find no evidence at large compactification radius that
tachyons enhance the tunneling rate. For the interesting radii, of order the
string scale, the question is difficult to answer due to the failure of the
expansion.Comment: 15 pages, 2 figures, Late
Relativistic Quantum Gravity at a Lifshitz Point
We show that the Horava theory for the completion of General Relativity at UV
scales can be interpreted as a gauge fixed theory, and it can be extended to an
invariant theory under the full group of four-dimensional diffeomorphisms. In
this respect, although being fully relativistic, it results to be locally
anisotropic in the time-like and space-like directions defined by a family of
irrotational observers. We show that this theory propagates generically three
degrees of freedom: two of them are related to the four-dimensional
diffeomorphism invariant graviton (the metric) and one is related to a
propagating scalar mode. Finally, we note that in the present formulation,
matter can be consistently coupled to gravity.Comment: v4: Erratum added: explanation on the true dynamical fields of the
relativistic theory added. The theory is interpreted as a Tensor-Scalar
relativistic theory. Reference added. Version accepted in JHE
G2 Hitchin functionals at one loop
We consider the quantization of the effective target space description of
topological M-theory in terms of the Hitchin functional whose critical points
describe seven-manifolds with G2 structure. The one-loop partition function for
this theory is calculated and an extended version of it, that is related to
generalized G2 geometry, is compared with the topological G2 string. We relate
the reduction of the effective action for the extended G2 theory to the Hitchin
functional description of the topological string in six dimensions. The
dependence of the partition functions on the choice of background G2 metric is
also determined.Comment: 58 pages, LaTeX; v2: Acknowledgments adde
Translation of the FMR1 mRNA is not influenced by AGG interruptions
The fragile X mental retardation 1 (FMR1) gene contains a CGG-repeat element within its 5′ untranslated region (5′UTR) which, for alleles with more than ∼40 repeats, increasingly affects both transcription (up-regulation) and translation (inhibition) of the repeat-containing RNA with increasing CGG-repeat length. Translational inhibition is thought to be due to impaired ribosomal scanning through the CGG-repeat region, which is postulated to form highly stable secondary/tertiary structure. One striking difference between alleles in the premutation range (55–200 CGG repeats) and those in the normal range (<∼40 repeats) is the reduced number/absence of ‘expansion stabilizing’ AGG interruptions in the larger alleles. Such interruptions, which generally occur every 9–11 repeats in normal alleles, are thought to disrupt the extended CGG-repeat hairpin structure, thus facilitating translational initiation. To test this hypothesis, we have measured the translational efficiency of CGG-repeat mRNAs with 0–2 AGG interruptions, both in vitro (rabbit reticulocyte lysates) and in cell culture (HEK-293 cells). We demonstrate that the AGG interruptions have no detectable influence on translational efficiency in either a cell-free system or cell culture, indicating that any AGG-repeat-induced alterations in secondary/tertiary structure, if present, do not involve the rate-limiting step(s) in translational initiation
Colitis and Colon Cancer in WASP-Deficient Mice Require Helicobacter Species
Background: Wiskott–Aldrich syndrome protein–deficient patients and mice are immunodeficient and can develop inflammatory bowel disease. The intestinal microbiome is critical to the development of colitis in most animal models, in which Helicobacter spp. have been implicated in disease pathogenesis. We sought to determine the role of Helicobacter spp. in colitis development in Wiskott–Aldrich syndrome protein–deficient (WKO) mice.
Methods: Feces from WKO mice raised under specific pathogen-free conditions were evaluated for the presence of Helicobacter spp., after which a subset of mice were rederived in Helicobacter spp.–free conditions. Helicobacter spp.–free WKO animals were subsequently infected with Helicobacter bilis.
Results: Helicobacter spp. were detected in feces from WKO mice. After rederivation in Helicobacter spp.–free conditions, WKO mice did not develop spontaneous colitis but were susceptible to radiation-induced colitis. Moreover, a T-cell transfer model of colitis dependent on Wiskott–Aldrich syndrome protein–deficient innate immune cells also required Helicobacter spp. colonization. Helicobacter bilis infection of rederived WKO mice led to typhlitis and colitis. Most notably, several H. bilis–infected animals developed dysplasia with 10% demonstrating colon carcinoma, which was not observed in uninfected controls.
Conclusions: Spontaneous and T-cell transfer, but not radiation-induced, colitis in WKO mice is dependent on the presence of Helicobacter spp. Furthermore, H. bilis infection is sufficient to induce typhlocolitis and colon cancer in Helicobacter spp.–free WKO mice. This animal model of a human immunodeficiency with chronic colitis and increased risk of colon cancer parallels what is seen in human colitis and implicates specific microbial constituents in promoting immune dysregulation in the intestinal mucosa.National Institutes of Health (U.S.) (R01OD011141)National Institutes of Health (U.S.) (R01CA067529)National Institutes of Health (U.S.) (P01CA026731)National Institutes of Health (U.S.) (P30ES02109
Gravitational renormalization of quantum field theory: a "conservative" approach
We propose general guidelines in order to incorporate the geometrical
description of gravity in quantum field theory and address the problem of UV
divergences non-perturbatively. In our aproach, each virtual particle in a
Feynman graph should be described by a modified propagator and move in the
space-time generated by the other particles in the same graph according to
Einstein's (semiclassical) equations.Comment: 7 pages, talk given at DICE 200
Killing-Yano equations and G-structures
We solve the Killing-Yano equation on manifolds with a -structure for
and . Solutions
include nearly-K\"ahler, weak holonomy , balanced SU(n) and holonomy
manifolds. As an application, we find that particle probes on
compactifications of type IIA and 11-dimensional supergravity admit a -type of symmetry generated by the fundamental forms. We also explore the
-symmetries of string and particle actions in heterotic and common
sector supersymmetric backgrounds. In the heterotic case, the generators of the
-symmetries completely characterize the solutions of the gravitino
Killing spinor equation, and the structure constants of the -symmetry
algebra depend on the solution of the dilatino Killing spinor equation.Comment: 10 pages, minor change
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