8,492 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-
Initiating a Swine Production Medicine Program
The role of veterinary medicine in the United States food animal industry is currently changing. Veterinarians are no longer viewed as mere providers of clinical services such as healing individual sick animals. This traditional role is being replaced with planned animal health programs for the entire herd. The objective of production medicine is to consistently maintain overall animal health and increase production cost-effectively to attain optimum economic returns for the producer. This holistic approach to animal health and production reduces the importance of specific infectious agents per se, and concentrates on the effect of interactions of these agents, environment, nutrition, genetics, and management on animal performance. Attempting to assimilate all these factors, in hopes of developing specific recommendations for the producer, may seem overwhelming when starting a production medicine program. This case report will illustrate the diagnostic procedures used to evaluate these factors when initiating a program for a swine herd in central Iowa
Analogy, Dirac-Majorana Neutrino Duality and the Neutrino Oscillations
The intent of this paper is to convey a new primary physical idea of a
Dirac-Majorana neutrino duality in relation to the topical problem of neutrino
oscillations. In view of the new atmospheric, solar and the LSND neutrino
oscillation data, the Pontecorvo oscillation analogy is generalized
to the notion of neutrino duality with substantially different physical meaning
ascribed to the long-baseline and the short-baseline neutrino oscillations. At
the level of CP-invariance, the suggestion of dual neutrino properties defines
the symmetric two-mixing-angle form of the widely discussed four-neutrino
-mixing scheme, as a result of the lepton charge conservation selection
rule and a minimum of two Dirac neutrino fields. With neutrino duality, the
two-doublet structure of the Majorana neutrino mass spectrum is a vestige of
the two-Dirac-neutrino origin. The fine neutrino mass doublet structure is
natural because it is produced by a lepton charge symmetry violating
perturbation on a zero-approximation system of two twofold mass-degenerate
Dirac neutrino-antineutrino pairs. A set of inferences related to the neutrino
oscillation phenomenology in vacuum is considered.Comment: 13 pages, LaTeX. Minor modifications, new references adde
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
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
Vacuum defects without a vacuum
Topological defects can arise in symmetry breaking models where the scalar
field potential has no minima and is a monotonically decreasing
function of . The properties of such vacuumless defects are quite
different from those of the ``usual'' strings and monopoles. In some models
such defects can serve as seeds for structure formation, or produce an
appreciable density of mini-black holes.Comment: 11 pages, REVTeX, 1 Postscript figure. Minor changes. Final version,
to appear in Phys. Rev.
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