Showing papers on "Cosmology published in 1984"
TL;DR: In this article, it was shown that in a simple minisuperspace model this boundary condition leads to a wave function which can be interpreted as a superposition of quantum states which are peaked around a family of classical solutions of the field equations.
628 citations
TL;DR: In this paper, the authors derived similarity solutions which describe the collapse of cold, collisionless matter in a perturbed Einstein-de Sitter universe, and they obtained three classes of solutions, one each with planar, cylindrical, and spherical symmetry.
Abstract: We derive similarity solutions which describe the collapse of cold, collisionless matter in a perturbed Einstein-de Sitter universe. We obtain three classes of solutions, one each with planar, cylindrical, and spherical symmetry. Our solutions can be computed to arbitrary accuracy, and they follow the development of structure in both the linear and nonlinear regimes.
528 citations
TL;DR: In this paper, a set of models from local and high-redshift observations were compared to the Friedmann-Lemaitre cosmological constant π 1.0.
Abstract: The inflationary scenario requires that the universe have negligible curvature along constant-density surfaces. In the Friedmann-Lemaitre cosmology that leaves us with two free parameters, Hubble's constant H/sub 0/ and the density parameter ..cap omega../sub 0/ (or, equivalently, the cosmological constant ..lambda..). I discuss here tests of this set of models from local and high-redshift observations. The data agree reasonably well with ..cap omega../sub 0/approx.0.2.
452 citations
TL;DR: In this article, it was shown that cosmic strings would generate anisotropy of the microwave background temperature with a very distinctive feature; the temperature would have steplike discontinuities on curves on the sky.
Abstract: There has been much interest in the cosmological consequences of line-like topological defects (‘cosmic strings’) which may be produced in a phase transition in the early Universe1–8. Such strings would produce density fluctuations on a broad range of scales and may have been responsible for the formation of galaxies. In view of this possibility, it would be useful to have more direct evidence of the existence of strings than the observed clustering of matter. We show here that cosmic strings would generate anisotropy of the microwave background temperature with a very distinctive feature; the temperature would have steplike discontinuities on curves on the sky. Present anisotropy measurements limit the line density parameter, Gμ to be <10−5. Popular values of this parameter, for the purpose of galaxy formation, are only an order of magnitude below this. The anisotropy that we discuss will exist in addition to that produced by curvature fluctuations due to strings and matter at the time that the Universe becomes optically thin.
388 citations
01 Jan 1984
TL;DR: According to present cosmology, certain stars end their careers in a total gravitational collapse that transcends the ordinary laws of physics as mentioned in this paper, which is known as a total geyser collapse.
Abstract: According to present cosmology, certain stars end their careers in a total gravitational collapse that transcends the ordinary laws of physics.
348 citations
TL;DR: In this article, it was shown that the predicted number of low-energy cosmic-ray antiprotons is comparable to the observed flux of cosmic rays and gamma rays in the galactic halo and that the cosmological photino density and the masses of scalar quarks and leptons determined the present annihilation rate.
Abstract: Observational tests of the hypothesis that the universe is flat and dominated by dark matter in the form of massive photinos include the production of significant fluxes of cosmic rays and gamma rays in our galactic halo. Specification of the cosmological photino density and the masses of scalar quarks and leptons determines the present annihilation rate. The predicted number of low-energy cosmic-ray antiprotons is comparable to the observed flux.
294 citations
01 Jan 1984
TL;DR: In this article, the authors make only passing reference to astrophysical aspects of cosmology, and such features as GUTS, quantum gravity, etc., which are covered in depth in recent reviews, e.g., Gibbons, Hawking and Siklos, 1983; Royal Society 1983.
Abstract: This paper discusses General Relativistic Aspects of Cosmology. Thus it will make only passing reference to astrophysical aspects of cosmology, and such features as GUTS, quantum gravity, etc. (these are covered in depth in recent reviews, e.g. Balian et al., 1980; Gibbons, Hawking and Siklos, 1983; Royal Society 1983).
273 citations
248 citations
TL;DR: In this article, a revised model of the inflationary universe under the framework of Brans-Dicke theory is proposed, and it is shown that the scale factor of the universe during the inflation varies as R approximately tw+1/2 and not exponentially, but still it gives rise to enough inflation to solve the cosmological puzzles.
Abstract: A revised model of the inflationary universe under the framework of Brans-Dicke theory is proposed. It is shown that the scale factor of the universe during the inflation varies as R approximately tw+1/2 and not exponentially, but still it gives rise to enough inflation to solve the cosmological puzzles. It is found that the quantum gravity effects come into play in the same scale as that of grand unified theories (i.e. at T approximately 1014 GeV) rather than at T approximately 1019 GeV, hence providing a natural solution to the 'milder version' of the flatness problem inherent in the conventional inflationary scenarios. This scenario also provides a simple way to estimate theoretically the present value of the gravitational constant. The estimated value agrees well with the actual value despite many approximations and the ignorance of quantum gravity; the difference is only by a factor of the order of 10-2.
192 citations
TL;DR: In this paper, the cosmological consequences of elementary particle theories based on spontaneously broken N = 1 supergravity are investigated, and it is shown that in most of the theories this conflict is not resolved even with the help of inflation.
168 citations
TL;DR: In this article, the authors developed a new theory for galaxy clustering in an expanding universe based on the thermodynamics of gravitating systems and applied to the highly nonlinear regime of strong clustering.
Abstract: We develop a new theory for galaxy clustering in an expanding universe. It is based on the thermodynamics of gravitating systems and applies to the highly nonlinear regime of strong clustering. There are no free parameters in the simplest form of this theory. It predicts distribution functions of all orders, from voids to hundreds of galaxies. Comparison of these predictions with the results of numerical N-body experiments shows substantial agreement. Comparison with the observed distribution of galaxies may determine whether it has unrelaxed structure that retains information from much easier epochs of the universe.
TL;DR: In this paper, the authors considered a class of spatially homogeneous, anisotropic, perfect fluid, cosmological models in 1 + d + D + D dimensions (d, D arbitrary) and showed that these models can lead to universes with 3 dimensions expanding and D contracting.
TL;DR: The evolution of a universe with π = 1 which becomes dominated by relatively light, non-intercommuting strings at redshift z/sub s/ is similar to that of a matter-dominated universe with Ω(2 + π π + ρ − 1/1/<1) as mentioned in this paper.
Abstract: The evolution of a universe with ..cap omega.. = 1 which becomes dominated by relatively light, non-intercommuting strings at redshift z/sub s/ is similar to that of a matter-dominated universe with ..cap omega..approx.(2+z/sub s/)/sup -1/<1. The existence of such strings can resolve the conflict between the ..cap omega.. = 1 prediction of inflationary cosmology and observations.
TL;DR: In this article, an inflationary model which satisfies constraints from particle physics and cosmology is presented, and the key feature is an SU(5)-singlet field which drives inflation, leads to proper density fluctuations, and solves the strong CP problem by the invisible axion mechanism.
Abstract: An inflationary model which satisfies constraints from particle physics and cosmology is presented. The key feature is an SU(5)-singlet field which drives inflation, leads to proper density fluctuations, and solves the strong CP problem by the invisible axion mechanism. Thus, for the first time, all reservations about the inflationary universe are removed.
TL;DR: In this paper, the growth of energy-density perturbations in inflationary-universe models, applying an extension of Bardeen's gauge-invariant framework derived in a previous paper, was studied.
Abstract: We study the growth of energy-density perturbations in inflationary-universe models, applying an extension of Bardeen's gauge-invariant framework derived in a previous paper. The complete analysis is exemplified in the case of the ''new inflationary universe'' of Linde and Albrecht and Steinhardt. For this model we obtain the following result: the amplitude of energy-density fluctuations at horizon crossing is of order 50, far too large to match with the usual pictures of galaxy formation. Our result agrees with other published analyses. We conclude that the amplification of energy-density perturbations is determined by the change in the equation of state between initial and final Hubble radius crossing. It is, however, independent of the phase structure between the two crossings. In particular, it is independent of the reheating mechanism. We also derive a simple formula which describes the complete evolution of perturbations outside the horizon whenever entropy and anisotropic stress perturbations are unimportant. Finally, we comment on previous published methods and discuss their limitations.
TL;DR: In this paper, a class of grand-unified theories in which cosmologically significant axion and neutrino energy densities arise naturally is considered, and attention is given to (1) an inflationary scenario, (2) inflation followed by string production, and (3) a noninflationary scenario with density fluctuations caused solely by strings.
Abstract: A class of grand-unified theories in which cosmologically significant axion and neutrino energy densities arise naturally is considered. To obtain large-scale structure, attention is given to (1) an inflationary scenario, (2) inflation followed by string production, and (3) a noninflationary scenario with density fluctuations caused solely by strings. It is shown that inflation may be compatible with the recent observational indications that Omega less than 1 on the scale of superclusters, particularly if strings are present.
TL;DR: A quasi-Newtonian calculation adapted from Newtonian cosmology suggests that a 'Milgrom universe' will recollapse even if the classical closure parameter Omega is much less than unity as mentioned in this paper.
Abstract: Milgrom's (1983) recent revision of Newtonian dynamics was introduced to eliminate the inference that large quantities of invisible mass exist in galaxies. It is shown by simple examples that a Milgrom acceleration, in the form presented so far, implies other far-reaching changes in dynamics. The momentum of an isolated system is not conserved, and the usual theorem for center-of-mass motion of any system does not hold. Naive applications require extreme caution. The model fails to provide a complete description of particle dynamics and should be thought of as a revision of Kepler's laws rather than Newton's. The Milgrom acceleration also implies fundamental changes in cosmology. A quasi-Newtonian calculation adapted from Newtonian cosmology suggests that a 'Milgrom universe' will recollapse even if the classical closure parameter Omega is much less than unity. The solution, however, fails to satisfy the cosmological principle. Reasons for the breakdown of this calculation are examined. A new theory of gravitation will be needed before the behavior of a Milgrom universe can be predicted.
TL;DR: In this paper, the evolution of the population of a coupled system of two neutral fermions in which the lighter one is stable is studied using the standard model of cosmology.
TL;DR: In this article, it was shown that the existence of majorons, which enable a heavy neutrino, 500 eV ≲ mνH ≲ 25 keV to decay into light neutrinos mνL ≲ 8 eV and a majoron, with lifetime 104 yr ≲ τνH = 108 yr can solve both the large and small scale dark matter problems.
TL;DR: In this article, the authors derived similarity solutions which describe the evolution of spherically symmetric voids in a perturbed Einstein-de Sitter universe filled with cold, collisionless matter.
Abstract: We derive similarity solutions which describe the evolution of spherically symmetric voids in a perturbed Einstein-de Sitter universe filled with cold, collisionless matter. The character of a solution depends upon the profile of the initial density deficit. Gradual perturbations give rise to holes within which the density rises smoothly to the background value. Steep perturbations result in voids bounded by overdense shells with sharp edges, i.e., collisionless gravitational shocks.
Journal Article•
TL;DR: In this paper, the behavior of quantized fields in the process of tunneling a closed homogeneous isotropic universe is examined and it is shown that tunneling of the universe from the Friedman regime to the de Sitter regime is accompanied by catastrophic creation of particles.
Abstract: The problem of the behavior of quantized fields in the process of tunneling of a closed homogeneous isotropic universe is examined. It is shown that tunneling of the universe from the Friedman regime to the de Sitter regime is accompanied by catastrophic creation of particles.
TL;DR: In this paper, a lower bound on root-mean-square fluctuations (ΔTr.m.s) at an angular scale of ∼4 arc min to 2.1 × 10−5 at the 95% confidence level was established.
Abstract: As a remnant of the early Universe, the cosmic microwave background provides unique information on the initial conditions from which matter has evolved to form the structures we see today. All efforts to detect small-scale structure in this radiation have so far been unsuccessful (ref. 1 and refs therein)1–4. Nevertheless, upper limits set on possible underlying fluctuations restrict the range of physical models for perturbations of the density in the early Universe. Our search for small-scale anisotropy in the background radiation has now resulted in a lowering of the upper limit on root-mean-square fluctuations (ΔTr.m.s) observed at an angular scale of ∼4 arc min to ΔTr.m.s./T<2.1 × 10−5 at the 95% confidence level (where T = 2.7 K, the temperature of the background radiation). The actual limits deduced from our experiment depend on the model assumed for the unseen fluctuations. Several possibilities are discussed as well as the implications this new measurement has for various cosmological models.
TL;DR: In this article, the authors present a classical field theory which has a long epoch resembling the Friedmann universe despite the presence of a large negative cosmological constant in its most plausible realization, which involves a massive third-rank antisymmetric-tensor gauge field.
Abstract: We present a classical field theory which has a long epoch resembling the Friedmann universe despite the presence of a large negative cosmological constant In its most plausible realization the model involves a massive third-rank antisymmetric-tensor gauge field To be consistent with standard cosmology the mass must be extremely small and the only reasonable mechanism for generating it is a semiclassical tunneling effect
KEK1
TL;DR: In this article, it was shown that above a critical temperature the effective gravitational constant becomes negative if the extra dimension is large enough, which may explain how the extra space has decoupled from the general expansion.
Abstract: The quantum effective action is computed at finite temperatures in a Robertson-Walker type of metric suggested in Kaluza-Klein theories. The most interesting result is that above a critical temperature the effective gravitational constant becomes negative if the extra dimension is large enough. This provides a mechanism for the bounce from a contracting phase and may explain how the extra space has decoupled from the general expansion. The bounce mechanism also leads to a picture of the recycling universe, in which entropy produced after many cycles of expansion and contraction may solve the horizon and the flatness problem of the standard cosmology.
TL;DR: In this paper, a solution de Tolman for un modele ferme heterogene rempli de matiere without pression is presented. But this solution is not suitable for a region localement ouverte dans un univers ferme.
Abstract: Etude de l'evolution dynamique d'une region localement ouverte dans un univers ferme. On utilise une solution de Tolman pour un modele ferme heterogene rempli de matiere sans pression
TL;DR: In this paper, the vacuum state wave functional of a free scalar field in the de Sitter phase of an inflationary universe is used to calculate the classical matter perturbations which couple to gravity.
TL;DR: The neutrino-dominated universe appears to conflict with observation irrespective of the details of the processes which govern galaxy formation as discussed by the authors, however, their X-ray emission would make them highly visible if more than 2.5 percent of their mass was in ordinary matter.
Abstract: Quite soon after the first collapse of structure, almost half the matter in a neutrino-dominated universe is expected to reside in clusters. The masses and binding energies of these neutrino clusters are too large for them to be identified with observed galaxy clusters. Even if such objects were able to suppress all galaxy formation, their X-ray emission would, however, make them highly visible if more than 2.5 percent of their mass was in ordinary matter. Such a low baryon density leads to insuffient cooling for galaxies to form in pancakes. A neutrino-dominated universe appears to conflict with observation irrespective of the details of the processes which govern galaxy formation.