Showing papers on "Particle horizon published in 1982"

Reheating an inflationary universe

Abstract: A numerical analysis of the evolution of the Higgs expectation value and the temperature of the universe during the symmetry-breaking phase transition in an SU(5) theory with radiatively induced symmetry breaking is presented. It is shown that there is sufficient inflation (exponential expansion) to explain the cosmological homogeneity, isotropy, flatness, and monopole puzzles, and also that the universe reheats to a temperature $O({10}^{14} \mathrm{GeV})$ so that the usual scheme for baryogenesis can proceed.

Gravitational Effects upon Cosmological Phase Transitions

Abstract: The effects of spacetime curvature upon phase transitions in an expanding universe are investigated. We consider a Robertson-Walker model which is a radiation-dominated universe at early times and becomes de Sitter space at later times. In this universe the stability of a field theory containing a pair of interacting scalar fields is studied in first-order perturbation theory. It is noted that the crucial quantity in the stability analysis is $〈{\ensuremath{\varphi}}^{2}〉$, where $\ensuremath{\varphi}$ is a free scalar field. The behavior of $〈{\ensuremath{\varphi}}^{2}〉$ as a function of time is investigated, where both thermal and vacuum contributions are taken into account. It is shown that this behavior can be strongly affected by the coupling to the background gravitational field. Such coupling can cause $〈{\ensuremath{\varphi}}^{2}〉$ to decrease more slowly or even grow as the universe expands. This behavior can alter the evolution of the system and can result in either stabilization of an otherwise unstable field configuration or destabilization of an otherwise stable configuration.

Origin of the Universe as a quantum tunneling event

Abstract: We present a nonsingular model of cosmogenesis in which the Universe arises as a result of quantum-mechanical barrier penetration. The Universe is described throughout its evolution by a Friedmann-Robertson-Walker (FRW) metric, and the matter distribution by a perfect fluid, whose equation of state is chosen so as to allow the tunneling to occur. Cosmic evolution proceeds in three stages; an initial static spacetime configuration tunnels into a "fireball" state in which particle creation occurs. As the fireball expands, particle creation ends, and the Universe enters the "post-big-bang" epoch of adiabatic expansion. We find that within the context of the FRW ansatz, only a spatially closed universe may originate in this manner. Implications of this creation scheme and possible generalizations are discussed. As a by-product of this investigation we find that the evolution of the Universe is described by a Gell-Mann---Low equation with the $\ensuremath{\beta}$ function specified by the equation of state.

Nonsingular regenerating inflationary universe

Abstract: A new version of the inflationary universe scenario is suggested which provides a possible solution of the cosmological singularity problem

Geodesic instability and internal time in relativistic cosmology

Abstract: The concept of "internal time" is applied to a cosmological model having spatial hypersurfaces of negative curvature. It is then possible to ascribe an irreversible evolution to the expanding universe without resorting to any "coarse graining" or "loss of information." The key observation which enables this description to be used is that geodesic flow on a four-manifold can be reduced to geodesic flow on a three-manifold when the Robertson-Walker metric is used. If the three-surface is compactified in such a way as not to change the metric, and if it has negative curvature, the geodesic system is a Bernoulli flow a dynamical system which has the highest degree of instability. We draw various conclusions about mixing in the system pertinent to the microwave background, the observational consequences of negative curvature for objects moving with respect to the galaxies, and we show that the requirement of negative curvature always leads to a particle horizon, a conclusion which has some bearing on the physical spectrum of the internal time operator and on the possibility of removing the cosmological singularity to the infinite past. © 1982 The American Physical Society.

Horizon-free universe

Abstract: We have studied a theory of gravity, consistent with all astronomical observations, which is an extension of general relativity generated by a gravitational field Lagrangian proportional to $R+A{R}^{2}$ (where $R$ is the scalar curvature and $A$ is a new dimensional constant). We find cosmological solutions without a particle horizon for any value of $A$, compatible with cosmological observations if $A$ is negative and small enough. It is pointed out that while alleviating the problem of the large-scale physical uniformity of the universe, the theory may also alleviate the problem of the development of smaller-scale structures from an initially isotropic state, and possibly the problem of "hidden mass."

Cosmological spatial curvature probed by microwave polarization

Abstract: If there is a large-scale anisotropy in the expansion of the Universe, the microwave background radiation is expected to be linearly polarized. This Communication shows that spatial curvature is capable of rotating the polarization of the microwaves relative to its direction at last scattering, which is directly correlated with the expansion anisotropy (and so also the observed intensity anisotropy). In Friedmann-Robertson-Walker models of the Universe with additional small expansion anisotropy, the observed rotation relative to the intensity anisotropy would be appreciable and constant over the celestial sphere in the closed (type IX) model, but in the flat and open models, it must either vanish (types I and V) or vary in a complicated way over the celestial sphere (type ${\mathrm{VII}}_{h}$). These facts suggest a clear observational test of the closure of the Universe. Also, an ambiguity inherent in the homogeneity of the Universe does not allow prediction of the direction of rotation; thus homogeneous universes possess a property which might be called "handedness."

Phase transitions and dynamics of the Universe

Abstract: The restoration of symmetry at grand unification in a closed contracting Robertson-Walker universe could slow down and halt the contraction, causing the universe to bounce and avoid the singular state or the big crunch. During subsequent expansion the symmetry is broken and the universe reverts back to its present state. A scenario is presented whereby the present entropy of the substance is created through a series of such bounces along with three possible initial states. The monopole, horizon, and flatness difficulties faced in ordinary Big Bang models are also solved by the model presented.

Statistical Effect of Interactions on Particle Creation in Expanding Universe

Abstract: The statistical effect of interactions which drives many-particle systems toward equilibrium is expected to change the qualitative and quantitative features of particle creation in expanding universe. To investigate this problem a simplified model called the finite-time reduction model is formulated and applied to the scalar particle creation in the radiation dominant Friedmann universe. The number density of created particles and the entropy production due to particle creation are estimated. The result for the number density is compared with that in the conventional free field theory. It is shown that the statistical effect increases the particle creation and lengthens the active creation period. As for the entropy production it is shown that it is negligible for scalar particles in the Friedmann universe.

Newtonian cosmology and Friedmann's equation

Abstract: Models of the expansion of the Universe can be derived from Newton's laws by the methods of hydrodynamics. The author shows that if the galaxies are regarded as discrete particles then an even simpler presentation is possible. It is also noted that a relativistic Universe which contains only a finite amount of matter may be indistinguishable, within the limits of observation, from a Friedmann Universe in which the total amount of matter is infinite.

The early universe in a generalized theory of gravitation

Abstract: The standard Friedmann–Robertson–Walker (FRW) big-bang model of the universe requires special initial conditions: the early universe is highly homogeneous and isotropic even though there exist causally disconnected regions (horizon problem). A plane symmetric (anisotropic) solution of a system of field equations in a generalized theory of gravitation, predicts the beginning of the universe as a vacuum instability at a specific fundamental time (which can be associated with the Planck time (tp)), after which matter is created as the universe begins to expand. At a time t = tc there is a singular expansion, the anisotropy vanishes, and the physical horizon becomes infinite. Thereafter the solution of the field equations goes over into the FRW model. Thus the special initial conditions of the FRW model at the big-bang singularity t = tc are predicted by the theory.

Multipole anisotropy of the cosmic background radiation in density wave models

Abstract: We study the anisotropy of the cosmic background radiation predicted by the density-wave models at scales > or approx. =10/sup 0/ and establish the connection of the mulitpole moments of the wave pattern with the corresponding multipoles in the angular distribution of the radiation. In open spaces, mulitpoles of order l>2 are shown to be important for long-wavelength perturbations (for a reasonable mulitpole content in the wave pattern) and to dominate for wavelengths much larger than the particle horizon. The interpretation of available expeirmental data in terms of perturbations of the size of the particle horizon is discussed, and a sensitive test involving the gradient of the anisotropy is suggested.

A Finite Temperature λϕ4 Model and De Sitter-Friedmann Phase Transition in the Early Universe

Abstract: In this paper, we propose a simple finite temperature λ4 cosmological model to show that a new type singularity free cosmological model could be established by taking a series of important quantum and statistical effects into consideration such as spontaneous symmetry breaking, trace anomaly and particle creation, symmetry restoration at high temperature through phase transition and others. To begin with, the state of the universe would be a cold singu1arity free and horizon free Beltrami-Anti de Sitter one rather than a hot one. Then associated with the, particle creation, the temperature would, become higher and higher and as soon. as the temperature reached a critical value, Tc, a second-order phase transition would take place and the universe would transfer to a hot radiation dominated Friedmann state.

Cosmological consequences of permanent quark confinement

Abstract: The Hagedorn model of hadronic matter was originally developed as an application of the bootstrap principle, but it is also a model which describes permanent quark confinement. Our remarkable prediction of the model is that hadronic matter cannot be heated beyond a finite maximum temperature (=T q). In a cosmic context,T q is the maximum temperature of the early universe; its existence follows simply by imposing the principle of permanent quark confinement. In the limitT →T q, the Hagedorn model is ambiguous about the size of the early universe and about the numerical value of the hadronic energy density. However, once the temperature constraint is accepted, the uncertainty principle and the principle of permanent quark confinement require the absence of the essential singularity at cosmic timet = 0. This initial condition for the early universe may be interpreted as due to a strong, short-range repulsive core in the interaction between quark pairs (evident at the hadron level, for example, as a nucleon-nucleon hard core). The parameters of the (qq) hard core are calculated from known characteristics of the universe. The results are: for the range,R qq≲0.07 fm; for the height, V0 ≈ 4.6·1014 GeV. It then follows that the « big bang » was soft and started at t = 0 with temperatureT q ≈ 1.6·1012K, radiusR min ≈1/2·1013 cm and hadronic mass density ϱmax ≈ 6·1016 gr/cm3.

The estimation of the mean density in the universe

Abstract: The mean density of matter, as estimated from deep optical samples of galaxies, is too low to close the Universe. However, some additional considerations do not exclude such a possibility.

Many-sheeted models of the Universe

Abstract: Several versions of the pulsating (many-sheeted) model of the Universe are described, in particular, a model with reversal of the arrow of time. It is pointed out that the reversal point may be a singularity or may correspond to maximal cosmological expansion. The smoothing out of inhomogeneities and the growth of entropy produced by baryon decay are discussed, as well as processes involving black holes. It is conjectured that black holes are absent in the cosmological expansion-contraction cycle preceding the present one, and that such exceptional cycles do occur periodically.

Time development of the free-quark-to-baryon ratio from the very early universe

Abstract: An attempt is made to estimate the quark-to-nucleon ratio under the assumption that the reported fractional charges are the unmatched relic quarks which failed to find quark or the unstable diquark partners to form nucleons. The time development of the quark-to-nucleon number density ratio from the very early universe is obtained from a rate equation for the process. The cross-section for the quark-nucleon transition is assumed to be inversely proportional to the square of the momentum and reaches the maximum value of the proton size as the temperature decreases, due to the expansion of the universe. If the quark-nucleon transition starts at 3/2kTi - 0.4 GeV, the process practically ends at 3/2kT ≏0.2 GeV, and the quark-to-nucleon ratio is ~10-(20/21) with a quark rest mass of 0.001 GeV≲m0c2 ≲10 GeV.