20 research outputs found
Wave Function of a Brane-like Universe
Within the mini-superspace model, brane-like cosmology means performing the
variation with respect to the embedding (Minkowski) time before fixing
the cosmic (Einstein) time . The departure from Einstein limit is
parameterized by the 'energy' conjugate to , and characterized by a
classically disconnected Embryonic epoch. In contrast with canonical quantum
gravity, the wave-function of the brane-like Universe is (i) -dependent,
and (ii) vanishes at the Big Bang. Hartle-Hawking and Linde proposals dictate
discrete 'energy' levels, whereas Vilenkin proposal resembles -particle
disintegration.Comment: Revtex, 4 twocolumn pages, 3 eps figures (accepted for publication in
Class. Quan. Grav.
Geodetic Brane Gravity
Within the framework of geodetic brane gravity, the Universe is described as
a 4-dimensional extended object evolving geodetically in a higher dimensional
flat background. In this paper, by introducing a new pair of canonical fields
{lambda, P_{lambda}}, we derive the quadratic Hamiltonian for such a brane
Universe; the inclusion of matter then resembles minimal coupling. Second class
constraints enter the game, invoking the Dirac bracket formalism. The algebra
of the first class constraints is calculated, and the BRST generator of the
brane Universe turns out to be rank-1. At the quantum level, the road is open
for canonical and/or functional integral quantization. The main advantages of
geodetic brane gravity are: (i) It introduces an intrinsic, geometrically
originated, 'dark matter' component, (ii) It offers, owing to the Lorentzian
bulk time coordinate, a novel solution to the 'problem of time', and (iii) It
enables calculation of meaningful probabilities within quantum cosmology
without any auxiliary scalar field. Intriguingly, the general relativity limit
is associated with lambda being a vanishing (degenerate) eigenvalue.Comment: 23 pages, 1 figure, minor change
Nucleation of Brane Universes
The creation of brane universes induced by a totally antisymmetric tensor
living in a fixed background spacetime is presented, where a term involving the
intrinsic curvature of the brane is considered. A canonical quantum mechanical
approach employing Wheeler-DeWitt equation is done. The probability nucleation
for the brane is calculated taking into account both an instanton method and a
WKB approximation. Some cosmological implications arose from the model are
presented.Comment: 19 pages, 2 figure
An Integration of Genome-Wide Association Study and Gene Expression Profiling to Prioritize the Discovery of Novel Susceptibility Loci for Osteoporosis-Related Traits
Osteoporosis is a complex disorder and commonly leads to fractures in elderly persons. Genome-wide association studies (GWAS) have become an unbiased approach to identify variations in the genome that potentially affect health. However, the genetic variants identified so far only explain a small proportion of the heritability for complex traits. Due to the modest genetic effect size and inadequate power, true association signals may not be revealed based on a stringent genome-wide significance threshold. Here, we take advantage of SNP and transcript arrays and integrate GWAS and expression signature profiling relevant to the skeletal system in cellular and animal models to prioritize the discovery of novel candidate genes for osteoporosis-related traits, including bone mineral density (BMD) at the lumbar spine (LS) and femoral neck (FN), as well as geometric indices of the hip (femoral neck-shaft angle, NSA; femoral neck length, NL; and narrow-neck width, NW). A two-stage meta-analysis of GWAS from 7,633 Caucasian women and 3,657 men, revealed three novel loci associated with osteoporosis-related traits, including chromosome 1p13.2 (RAP1A, p = 3.6×10−8), 2q11.2 (TBC1D8), and 18q11.2 (OSBPL1A), and confirmed a previously reported region near TNFRSF11B/OPG gene. We also prioritized 16 suggestive genome-wide significant candidate genes based on their potential involvement in skeletal metabolism. Among them, 3 candidate genes were associated with BMD in women. Notably, 2 out of these 3 genes (GPR177, p = 2.6×10−13; SOX6, p = 6.4×10−10) associated with BMD in women have been successfully replicated in a large-scale meta-analysis of BMD, but none of the non-prioritized candidates (associated with BMD) did. Our results support the concept of our prioritization strategy. In the absence of direct biological support for identified genes, we highlighted the efficiency of subsequent functional characterization using publicly available expression profiling relevant to the skeletal system in cellular or whole animal models to prioritize candidate genes for further functional validation