9,658 research outputs found
Cosmic Microwave Background Radiation Anisotropy Induced by Cosmic Strings
We report on a current investigation of the anisotropy pattern induced by
cosmic strings on the cosmic microwave background radiation (MBR). We have
numerically evolved a network of cosmic strings from a redshift of to
the present and calculated the anisotropies which they induce. Based on a
limited number of realizations, we have compared the results of our simulations
with the observations of the COBE-DMR experiment. We have obtained a
preliminary estimate of the string mass-per-unit-length in the cosmic
string scenario.Comment: 8 pages of TeX - [Color] Postscript available by anonymous ftp at
ftp://fnas08.fnal.gov:/pub/Publications/Conf-94-197-A, FERMILAB-Conf-94/197-
Pair Production of Topological anti de Sitter Black Holes
The pair creation of black holes with event horizons of non-trivial topology
is described. The spacetimes are all limiting cases of the cosmological
metric. They are generalizations of the dimensional black hole and have
asymptotically anti de Sitter behaviour. Domain walls instantons can mediate
their pair creation for a wide range of mass and charge.Comment: 4 pages, uses late
Anisotropy of the Cosmic Neutrino Background
The cosmic neutrino background (CNB) consists of low-energy relic neutrinos
which decoupled from the cosmological fluid at a redshift z ~ 10^{10}. Despite
being the second-most abundant particles in the universe, direct observation
remains a distant challenge. Based on the measured neutrino mass differences,
one species of neutrinos may still be relativistic with a thermal distribution
characterized by the temperature T ~ 1.9K. We show that the temperature
distribution on the sky is anisotropic, much like the photon background,
experiencing Sachs-Wolfe and integrated Sachs-Wolfe effects.Comment: 5 pages, 2 figures / updated references, discussion of earlier wor
The GALATEA Test-Facility for High Purity Germanium Detectors
GALATEA is a test facility designed to investigate bulk and surface effects
in high purity germanium detectors. A vacuum tank houses an infrared screened
volume with a cooled detector inside. A system of three stages allows an almost
complete scan of the detector. The main feature of GALATEA is that there is no
material between source and detector. This allows the usage of alpha and beta
sources as well as of a laser beam to study surface effects. A 19-fold
segmented true-coaxial germanium detector was used for commissioning
Large Angular Scale CMB Anisotropy Induced by Cosmic Strings
We simulate the anisotropy in the cosmic microwave background (CMB) induced
by cosmic strings. By numerically evolving a network of cosmic strings we
generate full-sky CMB temperature anisotropy maps. Based on maps, we
compute the anisotropy power spectrum for multipole moments . By
comparing with the observed temperature anisotropy, we set the normalization
for the cosmic string mass-per-unit-length , obtaining , which is consistent with all other
observational constraints on cosmic strings. We demonstrate that the anisotropy
pattern is consistent with a Gaussian random field on large angular scales.Comment: 4 pages, RevTeX, two postscript files, also available at
http://www.damtp.cam.ac.uk/user/defects/ to appear in Physical Review
Letters, 23 September 199
Comments on scalar-tensor representation of nonlocally corrected gravity
The scalar-tensor representation of nonlocally corrected gravity is
considered. Some special solutions of the vacuum background equations were
obtained that indicate to the nonequivalence of the initial theory and its
scalar-tensor representation.Comment: 6 pages, refs adde
On the width of the last scattering surface
We discuss the physical effects of some accelerated world models on the width
of the last scattering surface (LSS) of the cosmic microwave background
radiation (CMBR). The models considered in our analysis are X-matter (XCDM) and
a Chaplygin type gas. The redshift of the LSS does not depend on the kind of
dark energy (if XCDM of Chaplygin). Further, for a Chaplygin gas, the width of
the LSS is also only weakly dependent on the kind of scenario (if we have dark
energy plus cold dark matter or the unified picture).Comment: 10 pages, 1 figure, 2 tables, accepted to IJMP
Quantum Creation of Topological Black Hole
The constrained instanton method is used to study quantum creation of a
vacuum or charged topological black hole. At the level, the relative
creation probability is the exponential of a quarter sum of the horizon areas
associated with the seed instanton.Comment: Report-no change onl
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