Topic
Cosmology
About: Cosmology is a research topic. Over the lifetime, 18004 publications have been published within this topic receiving 631028 citations. The topic is also known as: physical cosmology & cosmologies.
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01 Sep 1983
TL;DR: In this article, the primordial adiabatic perturbations and the gravitational waves that would develop in the 1980 model of a nonsingular cosmology with an initial de Sitter quantum stage resulting from gravitational vacuum polarization were calculated.
Abstract: Spectra are calculated for the primordial adiabatic perturbations and the gravitational waves that would develop in the author's 1980 model of a nonsingular cosmology with an initial de Sitter quantum stage resulting from gravitational vacuum polarization. The gravitational-wave spectrum will be flat; the adiabatic-perturbation spectrum, nearly so. In that event the most promising way to detect large-scale temperature anisotropy in the cosmic microwave background would be to measure ..delta..T/T correlations over 5/sup 0/--10/sup 0/ angles.
354 citations
28 Nov 2003
TL;DR: In this paper, the authors review the major challenges for high-energy neutrino astrophysics, among which the nature of dark matter, the origin of cosmic rays, and the physics of extreme objects such as active galactic nuclei, gamma-ray bursts, pulsars, and supernova remnants are of prime importance.
Abstract: ▪ Abstract High-energy (>100 MeV) neutrino astrophysics enters an era of opportunity and discovery as the sensitivity of detectors approaches astrophysically relevant flux levels. We review the major challenges for this emerging field, among which the nature of dark matter, the origin of cosmic rays, and the physics of extreme objects such as active galactic nuclei, gamma-ray bursts, pulsars, and supernova remnants are of prime importance. Variable sources at cosmological distances allow the probing of neutrino propagation properties over baselines up to about 20 orders of magnitude larger than those probed by terrestrial long-baseline experiments. We review the possible astrophysical sources of high-energy neutrinos, which also act as an irreducible background to searches for phenomena at the electroweak and grand-unified-theory symmetry-breaking scales related to possible supersymmetric dark matter and topological defects. Neutrino astronomy also has the potential to discover previously unimagined high-...
353 citations
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TL;DR: The cosmological solutions of a recently proposed extension of General Relativity with a Lorentz-invariant mass term were explored in this article, where the same constraint that removes the Boulware-Deser ghost in this theory also prohibits the existence of homogeneous and isotropic cosmologies.
Abstract: We explore the cosmological solutions of a recently proposed extension of General Relativity with a Lorentz-invariant mass term We show that the same constraint that removes the Boulware-Deser ghost in this theory also prohibits the existence of homogeneous and isotropic cosmological solutions Nevertheless, within domains of the size of inverse graviton mass we find approximately homogeneous and isotropic solutions that can well describe the past and present of the Universe At energy densities above a certain crossover value, these solutions approximate the standard FRW evolution with great accuracy As the Universe evolves and density drops below the crossover value the inhomogeneities become more and more pronounced In the low density regime each domain of the size of the inverse graviton mass has essentially non-FRW cosmology This scenario imposes an upper bound on the graviton mass, which we roughly estimate to be an order of magnitude below the present-day value of the Hubble parameter The bound becomes especially restrictive if one utilizes an exact self-accelerated solution that this theory offers Although the above are robust predictions of massive gravity with an explicit mass term, we point out that if the mass parameter emerges from some additional scalar field condensation, the constraint no longer forbids the homogeneous and isotropic cosmologies In the latter case, there will exist an extra light scalar field at cosmological scales, which is screened by the Vainshtein mechanism at shorter distances
353 citations
TL;DR: In this article, the formation of the first stars and quasars marks the transformation of the universe from its smooth initial state to its clumpy current state, and the study of high-redshift sources is likely to attract major attention in observational and theoretical cosmology over the next decade.
Abstract: ▪ Abstract The formation of the first stars and quasars marks the transformation of the universe from its smooth initial state to its clumpy current state. In popular cosmological models, the first sources of light began to form at a redshift z = 30 and reionized most of the hydrogen in the universe by z = 7. Current observations are at the threshold of probing the hydrogen reionization epoch. The study of high-redshift sources is likely to attract major attention in observational and theoretical cosmology over the next decade.
351 citations