655 research outputs found
Conformal smectics and their many metrics
We establish that equally spaced smectic configurations enjoy an infinite-dimensional conformal symmetry and show that there is a natural map between them and null hypersurfaces in maximally symmetric spacetimes. By choosing the appropriate conformal factor it is possible to restore additional symmetries of focal structures only found before for smectics on flat substrates
Supersymmetry Breaking in Warped Geometry
We examine the soft supersymmetry breaking parameters in supersymmetric
theories on a slice of AdS_5 which generate the hierarchical Yukawa couplings
by dynamically localizing the bulk matter fields in extra dimension. Such
models can be regarded as the AdS dual of the recently studied 4-dimensional
models which contain a supersymmetric CFT to generate the hierarchical Yukawa
couplings. In such models, if supersymmetry breaking is mediated by the bulk
radion superfield and/or some brane chiral superfields, potentially dangerous
flavor-violating soft parameters can be naturally suppressed, thereby avoiding
the SUSY flavor problem. We present some models of radion-dominated
supersymmetry breaking which yield a highly predictive form of soft parameters
in this framework.Comment: 17 pages, no figures, uses JHEP clas
Accounting for Multiple Comparisons in a Genome-Wide Association Study (GWAS)
Background
As we enter an era when testing millions of SNPs in a single gene association study will become the standard, consideration of multiple comparisons is an essential part of determining statistical significance. Bonferroni adjustments can be made but are conservative due to the preponderance of linkage disequilibrium (LD) between genetic markers, and permutation testing is not always a viable option. Three major classes of corrections have been proposed to correct the dependent nature of genetic data in Bonferroni adjustments: permutation testing and related alternatives, principal components analysis (PCA), and analysis of blocks of LD across the genome. We consider seven implementations of these commonly used methods using data from 1514 European American participants genotyped for 700,078 SNPs in a GWAS for AIDS.
Results
A Bonferroni correction using the number of LD blocks found by the three algorithms implemented by Haploview resulted in an insufficiently conservative threshold, corresponding to a genome-wide significance level of α = 0.15 - 0.20. We observed a moderate increase in power when using PRESTO, SLIDE, and simpleⳠwhen compared with traditional Bonferroni methods for population data genotyped on the Affymetrix 6.0 platform in European Americans (α = 0.05 thresholds between 1 à 10-7 and 7 à 10-8).
Conclusions
Correcting for the number of LD blocks resulted in an anti-conservative Bonferroni adjustment. SLIDE and simpleâł are particularly useful when using a statistical test not handled in optimized permutation testing packages, and genome-wide corrected p-values using SLIDE, are much easier to interpret for consumers of GWAS studies
Self-gravitating domain walls and the thin-wall limit
We analyse the distributional thin wall limit of self gravitating scalar
field configurations representing thick domain wall geometries. We show that
thick wall solutions can be generated by appropiate scaling of the thin wall
ones, and obtain an exact solution for a domain wall that interpolates between
AdS_4 asymptotic vacua and has a well-defined thin wall limit.Solutions
representing scalar field configurations obtained via the same scaling but that
do not have a thin wall limit are also presented.Comment: 10 pages, revte
Collapsing Perfect Fluid in Higher Dimensional Spherical Spacetimes
The general metric for N-dimensional spherically symmetric and conformally
flat spacetimes is given, and all the homogeneous and isotropic solutions for a
perfect fluid with the equation of state are found. These
solutions are then used to model the gravitational collapse of a compact ball.
It is found that when the collapse has continuous self-similarity, the
formation of black holes always starts with zero mass, and when the collapse
has no such a symmetry, the formation of black holes always starts with a mass
gap.Comment: Class. Quantum Grav. 17 (2000) 2589-259
A Solution to the Hierarchy Problem with an Infinitely Large Extra Dimension and Moduli Stabilization
We construct a class of solutions to the Einstein's equations for dimensions
greater than or equal to six. These solutions are characterized by a
non-trivial warp factor and possess a non-compact extra dimension. We study in
detail a simple model in six dimensions containing two four branes. One of each
brane's four spatial directions is compactified. The hierarchy problem is
resolved by the enormous difference between the warp factors at the positions
of the two branes, with the standard model fields living on the brane with
small warp factor. Both branes can have positive tensions. Their positions, and
the size of the compact dimension are determined in terms of the fundamental
parameters of the theory by a combination of two independent and comparable
effects---an anisotropic contribution to the stress tensor of each brane from
quantum fields living on it and a contribution to the stress tensor from a bulk
scalar field. One overall fine tuning of the parameters of the theory is
required ---that for the cosmological constant.Comment: 16 pages 1 figure. Conclusion about naturalness of hierarchy without
bulk interactions changed. Section added on obtaining a natural hierarchy
with bulk scalar field. References added. Minor editin
Restoration of a Severely Impacted Riparian Wetland System - The Pen Branch Project
The Savannah River Swamp is a 3020 ha forested wetland on the floodplain of the Savannah River and is located on the Department of Energyâs Savannah River Site (SRS) near Aiken, SC (Fig. 1). Historically the swamp consisted ofapproximately 50% baldcypress-water tupelo stands, 40% mixed bottomland hardwood stands, and 10% shrub, marsh, and open water. Tributeries of the river were typical of Southeastern bottomland hardwood forests. The hydrology was controlled by flow from four creeks that drain into the swamp and by flooding of the Savannah River. Upstream dams on the Savannah River have caused some alteration of the water levels and timing of flooding within the floodplain(Schneider et al., 1989)
Universal contributions to scalar masses from five dimensional supergravity
We compute the effective Kahler potential for matter fields in warped
compactifications, starting from five dimensional gauged supergravity, as a
function of the matter fields localization. We show that truncation to zero
modes is inconsistent and the tree-level exchange of the massive gravitational
multiplet is needed for consistency of the four-dimensional theory. In addition
to the standard Kahler coming from dimensional reduction, we find the quartic
correction coming from integrating out the gravity multiplet. We apply our
result to the computation of scalar masses, by assuming that the SUSY breaking
field is a bulk hypermultiplet. In the limit of extreme opposite localization
of the matter and the spurion fields, we find zero scalar masses, consistent
with sequestering arguments. Surprisingly enough, for all the other cases the
scalar masses are tachyonic. This suggests the holographic interpretation that
a CFT sector always generates operators contributing in a tachyonic way to
scalar masses. Viability of warped su- persymmetric compactifications
necessarily asks then for additional contributions. We discuss the case of
additional bulk vector multiplets with mixed boundary conditions, which is a
partic- ularly simple and attractive way to generate large positive scalar
masses. We show that in this case successful fermion mass matrices implies
highly degenerate scalar masses for the first two generations of squarks and
sleptons.Comment: 23 pages. v2: References added, new section on effect of additional
bulk vector multiplets and phenomenolog
Dimension in a Radiative Stellar Atmosphere
Dimensional scales are examined in an extended 3+1 Vaidya atmosphere
surrounding a Schwarzschild source. At one scale, the Vaidya null fluid
vanishes and the spacetime contains only a single spherical 2-surface. Both of
these behaviors can be addressed by including higher dimensions in the
spacetime metric.Comment: to appear in Gen. Rel. Gra
Defects in Chiral Columnar Phases: Tilt Grain Boundaries and Iterated Moire Maps
Biomolecules are often very long with a definite chirality. DNA, xanthan and
poly-gamma-benzyl-glutamate (PBLG) can all form columnar crystalline phases.
The chirality, however, competes with the tendency for crystalline order. For
chiral polymers, there are two sorts of chirality: the first describes the
usual cholesteric-like twist of the local director around a pitch axis, while
the second favors the rotation of the local bond-orientational order and leads
to a braiding of the polymers along an average direction. In the former case
chirality can be manifested in a tilt grain boundary phase (TGB) analogous to
the Renn-Lubensky phase of smectic-A liquid crystals. In the latter case we are
led to a new "moire" state with twisted bond order. In the moire state polymers
are simultaneously entangled, crystalline, and aligned, on average, in a common
direction. In the moire state polymers are simultaneously entangled,
crystalline, and aligned, on average, in a common direction. In this case the
polymer trajectories in the plane perpendicular to their average direction are
described by iterated moire maps of remarkable complexity, reminiscent of
dynamical systems.Comment: plain TeX, (33 pages), 17 figures, some uufiled and included, the
remaining available at ftp://ftp.sns.ias.edu/pub/kamien/ or by request to
[email protected]
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