Showing papers on "Cosmology published in 1986"
787 citations
TL;DR: In this article, a variation avec les parametres qui gouvernent la transition de phase and les possibilites de son observation is proposed. André et al. propose une evaluation du spectre du fond stochastique resultant.
Abstract: La cavitation au cours d'une transition de phase du premier ordre peut avoir donne naissance a un rayonnement gravitationnel. On propose une evaluation du spectre du fond stochastique resultant, sa variation avec les parametres qui gouvernent la transition de phase et les possibilites de son observation
333 citations
TL;DR: In this article, a Brans-Dicke theory with a scalar-field-dependent cosmological term is considered and solutions of the field equations in a homogeneous and isotropic space-time are obtained and discussed.
Abstract: A Brans-Dicke theory is considered with a scalar-field-dependent cosmological term. Solutions of the field equations in a homogeneous and isotropic space-time are obtained and discussed.
308 citations
TL;DR: In this paper, a model of the universe with an additional term Λ ( x ) g μν in the energymomentum tensor is motivated and presented, which is completely determined by the assumption that the energy density ofthe universe equals its critical value.
261 citations
TL;DR: In this paper, the existence of a mirror universe of fermions and forces is shown to be impossible, and the possible existence of such a universe is thereby excluded, as shown in Figure 1.
140 citations
TL;DR: In this article, the authors derived an expression which relates the mean curvature of isodensity surfaces to the power spectrum of density fluctuations in the linear regime of Gaussian fluctuations with random phases.
Abstract: It has been suggested recently that the topology of a distribution of galaxies can be characterized by the mean Gaussian curvature per unit volume of surfaces of constant density. An expression is derived which relates the mean curvature of isodensity surfaces to the power spectrum of density fluctuations in the linear regime of Gaussian fluctuations with random phases. The result may be compared to real galaxy catalogs if the galaxy density is smoothed over scales larger than a correlation length. The implications of the result for understanding the large-scale structure of the universe are discussed.
124 citations
TL;DR: In this paper, the authors measured the redshifts and fluxes of 1,000 field galaxies with a median redshift of 0.5 and determined the density parameter Omega by measuring the volume element (to a scale factor H03) as a function of redshift.
Abstract: This letter reports a new measurement of the density parameter Omega, which is the mass density of the universe relative to the critical density. The authors have measured the redshifts and fluxes of 1,000 field galaxies with a median redshift of 0.5. With this sample they determine Omega by measuring the volume element (to a scale factor H03) as a function of redshift. The measurement is sensitive to any kind of matter, luminous or dark. It is found that Omega = 0.9 (+0.7, -0.5), consistent with the Einstein-de Sitter model (Lambda = 0, Omega = 1).
116 citations
TL;DR: An upper bound on the string tension is obtained: G or approx.
Abstract: The evolution of a system of cosmic strings is studied using an extended version of an analytic formalism introduced by Kibble. It is shown that, in a radiation-dominated universe, the fate of the string system depends sensitively on the fate of the closed loops that are produced by the interactions of very long strings. The strings can be prevented from dominating the energy density of the Universe only if there is a large probability (> or approx. =50%) that a closed loop will intersect itself and break up into smaller loops. A comparison with the numerical simulations of Albrecht and Turok indicates that the probability of self-intersection is indeed large enough to allow the energy density in strings to stabilize at a small fraction of the radiation density, but there is a potential problem with the gravitational radiation that is produced by the strings. If the string tension is too large, then the gravitational radiation will be so copious that it interferes with primordial nucleosynthesis. By assuming that the probability of self-intersection is less than 85%, as the comparison with the results of Albrecht and Turok indicates, an upper bound on the string tension is obtained: G or approx. =2 x 10 W) predicted for the cosmic-string theory of galaxy formation. This bound would become significantly lower if the probability of intersection is less than 85%.« less
112 citations
TL;DR: It is demonstrated that the recently discovered large-scale structure of the Universe (voids and filaments) can be explained by cosmic strings and the presence of pointlike structures (''knobs'') of masses >10/sup 7/M/sub cirdot/ in the vicinity of larger galaxies is predicted.
Abstract: We wish to demonstrate that the recently discovered large-scale structure of the Universe (voids and filaments) can be explained by cosmic strings. We also predict the presence of pointlike structures (''knobs'') of masses >10/sup 7/M/sub cirdot/ in the vicinity of larger galaxies. The present analysis is limited to order-of-magnitude estimates. A detailed analysis would necessarily have to go into the full nonlinear theory of the growth of fluctuations in the Universe.
101 citations
01 Jan 1986
TL;DR: In this article, a wide range of topics, ranging from particle physics to the physics of collapsed objects, are discussed, including active nuclei, jets, hydrodynamics, galaxy clusters and distribution; general relativity theory; cosmic x-and gamma sources; numerical astrophysics; star evolution; space telescope and astrophysics facilities; cosmic microwave background; quantum field theory and gravitation.
Abstract: These proceedings contain papers combining a wide range of topics, ranging from particle physics to the physics of collapsed objects. Included are discussions on cosmology and cosmological models; active nuclei, jets, hydrodynamics; galaxy clusters and distribution; general relativity theory; cosmic x- and gamma sources; numerical astrophysics; star evolution; space telescope and astrophysics facilities; cosmic microwave background; quantum field theory and gravitation.
TL;DR: In this paper, an example of a cosmological model with variable G and Λ is presented, in which there is no creation and in which the rest mass of matter particles is constant.
Abstract: It has recently been asserted that a universe with a time-varying gravitational “constant”G necessarily implies creation if the rest mass of matter particles is constant. It is shown that this is not necessarily true. An example of a cosmological model with variableG and Λ is presented, in which there is no creation and in which the rest mass of matter particles is constant.
TL;DR: This paper showed that the mean mass density of galaxies is only about one third of that predicted by the popular Einstein-de Sitter cosmological model, and that either conventional ideas about galaxy formation are wrong, or the EDS model is not a useful approximation.
Abstract: Observations of galaxy clustering indicate that the mean mass density is only about one-third of that predicted by the popular Einstein–de Sitter cosmological model. Theory and observation can be reconciled if there has been large-scale segregation of galaxies from mass, but the gravitational instability of the expanding universe would tend to destroy such a segregation. Thus either conventional ideas about galaxy formation are wrong, or the Einstein–de Sitter model is not a useful approximation.
TL;DR: In this paper, the authors compare le modele a "lumiere fatiguee" and l'univers en expansion, without evolution, avec q o =O, aux donnees d'observations, en utilisant quatre sortes de tests cosmologiques.
Abstract: On a compare le modele sans evolution, a «lumiere fatiguee» et l'univers en expansion, sans evolution, avec q o =O, aux donnees d'observations, en utilisant quatre sortes de tests cosmologiques. Le modele a «lumiere fatiguee» correspond mieux aux observations
TL;DR: It is shown that all but a small subset of the homogeneous models undergo inflation, so that if sufficient inflation occurs to solve the flatness-horizon problems the Universe today would still be very isotropic.
Abstract: The promise of the inflationary-universe scenario is to free the present state of the universe from extreme dependence upon initial data. Paradoxically, inflation is usually analyzed in the context of the homogeneous and isotropic Robertson-Walker cosmological models. It is shown that all but a small subset of the homogeneous models undergo inflation. Any initial anisotropy is so strongly damped that if sufficient inflation occurs to solve the flatness and horizon problems, the universe today would still be very isotropic.
TL;DR: In this article, a cosmology based on the Brans-Dicke theory with a cosmological term dependent in the scalar field is proposed, which does not suffer from any unnatural fine tuning in the very early Universe such as the horizon, homogeneity, isotropy and flatness problems and does not present any difficulty concerning the GUTs magnetic monopoles.
Abstract: We propose a cosmology based on the Brans-Dicke theory with a cosmological term dependent in the scalar field. It is shown the existence of a solution in a Robertson-Walker metric that does not suffer from any unnatural fine tuning in the very early Universe such as the horizon, homogeneity, isotropy and flatness problems and does not present any difficulty concerning the GUTs magnetic monopoles.
TL;DR: In this article, the apparent Local Group motion inferred from infrared observations of an all-sky sample of spiral galaxies is interpreted in terms of a large-scale streaming motion for these galaxies on a scale of 50 h -1 Mpc.
Abstract: The apparent Local Group motion inferred from infrared observations of an all-sky sample of spiral galaxies is interpreted in terms of a large-scale streaming motion for these galaxies on a scale of 50 h -1 Mpc. If this streaming is induced by large-scale density fluctuations, the fluctuations required are compatible with the observed distribution of luminous matter, but only in a closed universe. In the context of current speculation regarding non-baryonic particle species which may dominate the mass of the universe, this result seems to be inconsistent with cold dark matter models.
TL;DR: Assuming a Calabi-Yau compactification, cosmological solutions are presented in ten-dimensional, N=1 Yang-Mills supergravity theory with the curvature squared term (R2μνϱσ −4Rμν2 + R2) as discussed by the authors.
TL;DR: It is shown that any model that undergoes sufficient inflation will become isotropic on scales greater than the horizon today, and it takes a very long time for anisotropies to become visible in the observable part of the Universe.
Abstract: We study the effects of anisotropic cosmologies on inflation. By properly formulating the field equations it is possible to show that any model that undergoes sufficient inflation will become isotropic on scales greater than the horizon today. Furthermore, we shall show that it takes a very long time for anisotropies to become visible in the observable part of the Universe. It is interesting to note that the time scale will be independent of the Bianchi model and of the initial anisotropy.
TL;DR: In this paper, a modele for the formation d'objets induite par des boucles de cordons cosmiques dans un Univers domine par la matiere froide is presented.
Abstract: On presente un modele pour la formation d'objets induite par des boucles de cordons cosmiques dans un Univers domine par la matiere froide
TL;DR: Vacuum Friedmann-Robertson-Walker cosmological models are derived in Lyra's manifold and some properties of the solutions are discussed in this paper, in addition to the usual de Sitter universe.
Abstract: Vacuum Friedmann-Robertson-Walker cosmological models are derived in Lyra's manifold and some properties of the solutions are discussed. In addition to the usual de Sitter universe, several new solutions are obtained.
01 Jan 1986
TL;DR: The proceedings of the NATO Workshop on Nycleosynthesis, held in March 1985 in Les Arcs, France, are presented and discussed in this article, which assembles the most recent discoveries and progresses in the field.
Abstract: Nuclear astrophysics explains the formation of the chemical element and the evolution of the composition of observable matter. This topic is obviously related to various aspects of nuclear physics (nuclear cross-sections, nuclear excited states, masses and life times). It is also very closely linked to many aspects of particle physics: Big Bang theories, nature of the dark matter of the Universe, existence of quarked nuclei, etc. All theses aspects are presented and discussed in this book, which assembles the most recent discoveries and progresses in the field. It is the proceedings of the NATO Workshop on Nycleosynthesis, held in March 1985 in Les Arcs, France.
TL;DR: In this paper, the authors provided a completely quantum-mechanical derivation of the spectrum of gravitational waves produced in any inflationary cosmology and showed how the results depend on the initial state at the beginning of the inflationary period.
TL;DR: The Hartle-Hawking proposal for the boundary conditions of the universe is extended to six-dimensional Einstein-Maxwell theory in this paper, where a minisuperspace wave function is calculated and found, in the classical limit, to correspond to a superposition of classical solutions in which two of the dimensions remain small whilst the other four behave like an inflationary universe.
TL;DR: An empty Kantowski-Sachs universe model with a cosmological constant was found in this article, and the universe emerges from a pancake singularity at t = 0.
Abstract: An empty Kantowski-Sachs universe model with a cosmological constant is found. It emerges from a pancake singularity at t = 0. If the cosmological constant is of the same magnitude as that induced by a GUT vacuum phase transition, this universe enters an exponentially expanding era at the GUT time t/sub G/ = 1,0x10/sup -35/ sec. The universe then isotropizes rapidly, and the shear diminishes by a factor of 10/sup -56/ if this inflationary era lasts for t/sub 1/ = 1,3x10/sup -33/ sec, as is the case in Guth's inflationary universe model.
Journal Article•
[...]
TL;DR: A review of the basic equations and concepts of big bang cosmology are presented in this article, where it is shown that the universe cannot be closed by baryons and the universe is not closed by a singularity.
Abstract: A review of the basic equations and concepts of big bang cosmology are presented. It is shown that the universe cannot be closed by baryons. (DWL)
TL;DR: Observation and theory are coming tantalizingly close to measuring the elusive anisotropy, or to revealing that the authors' ideas about the origin of galaxies and large-scale structures are in need of substantial revision.
Abstract: Current hypotheses for the origin of structure in the Universe lead to predictions of the amplitudes of anisotropies in the cosmic microwave background radiation. The dipole anisotropy is related to density fluctuations on large scales and to other determinations of our motion relative to distant galaxies. Observation and theory are coming tantalizingly close to measuring the elusive anisotropy, or to revealing that our ideas about the origin of galaxies and large-scale structures are in need of substantial revision.