6 research outputs found
Normal modes for metric fluctuations in a class of higher-dimensional backgrounds
We discuss a gauge invariant approach to the theory of cosmological
perturbations in a higher-dimensonal background. We find the normal modes which
diagonalize the perturbed action, for a scalar field minimally coupled to
gravity, in a higher-dimensional manifold M of the Bianchi-type I, under the
assumption that the translations along an isotropic spatial subsection of M are
isometries of the full, perturbed background. We show that, in the absence of
scalar field potential, the canonical variables for scalar and tensor metric
perturbations satisfy exactly the same evolution equation, and we discuss the
possible dependence of the spectrum on the number of internal dimensions.Comment: 19 pages, LATEX, an explicit example is added to discuss the possible
dependence of the perturbation spectrum on the number of internal dimensions.
To apper in Class. Quantum Gra
Gravitational Violation of R Parity and its Cosmological Signatures
The discrete R-parity () usually imposed on the Supersymmetric (SUSY)
models is expected to be broken at least gravitationally. If the neutralino is
a dark matter particle its decay channels into positrons, antiprotons and
neutrinos are severely constrained from astrophysical observations. These
constraints are shown to be violated even for Planck-mass-suppressed
dimension-five interactions arising from gravitational effects. We perform a
general analysis of gravitationally induced violation and identify two
plausible and astrophysically consistent scenarios for achieving the required
suppression.Comment: 10 pages, no figure
Apolipoprotein E genotype and outcome in infants with hypoxic–ischemic encephalopathy
BACKGROUND: Adults with the apolipoprotein E gene (APOE) alleles e4 and e2 are at high risk of poor neurologic outcome after brain injury. The e4 allele has been associated with cerebral palsy and the e2 allele has been associated with worse neurologic outcome with congenital heart disease. This study was done to test the hypothesis that APOE genotype is associated with outcome among neonates who survive after hypoxic-ischemic encephalopathy (HIE). METHODS: We conducted a cohort study of infants who survived HIE and had 18 – 22 month standardized neurodevelopmental evaluations to assess associations between disability and APOE genotypes e3/e3, e4/-, and e2/- RESULTS: 139 survivors were genotyped. 86 (62%) were e3/e3, 41 (29%) were e4/-, and 14 (10%) were e2/-. 129 infants had genotype and follow-up data; 26% had moderate or severe disabilities. Disability prevalence was 30% and 19% among those with and without e3/e3 genotype, 25% and 26% among those with and without the e2 allele, and 18% and 29% among those with and without the e4 allele. None of the differences were statistically significant. Cerebral palsy prevalence was also similar among genotype groups. CONCLUSION: Disability was not associated with APOE genotype in this cohort of HIE survivors