Particle horizon

About: Particle horizon is a research topic. Over the lifetime, 2096 publications have been published within this topic receiving 69137 citations.

5D generalized inflationary cosmology

Abstract: We consider a 5D Kaluza-Klein type cosmological model with the fifth coordinate being a generalization of the invariant “historical” timeτ of the covariant theory of Horwitz and Piron. We distinguish between vacuum-, off-shell matter-, and on-shell matter-dominated eras as the solutions of the corresponding 5D gravitational field equations, and build an inflationary scenario according to which passage from the off-shell matter-dominated era to the on-shell one occurs, probably as a phase transition. We study the effect of this phase transition on the expansion rate in both cases of localO(4,1) andO(3,2) invariance of the extended (x µ,τ) manifold and show that it does not change in either case. The expansion of the model we consider is not adiabatic; the thermodynamic entropy is a growing function of cosmic time for the closed universe, and can be a growing function of historical time for the open and the flat universe. A complete solution of the 5D gravitational field equations is obtained for the on-shell matter-dominated universe. The open and the closed universe are shown to tend asymptotically to the standard 4D cosmological models, in contrast to the flat universe which does not have the corresponding limit. Finally, possible cosmological implications are briefly discussed.

Evolution of perturbations in a baryon-dominated universe - Gauge-invariant analysis

Abstract: The evolution of scalar (density) perturbations in a baryon-dominated universe is comprehensively studied on the basis of a gauge-invariant method. In particular, the residual anisotropies of the cosmic microwave background radiation are calculated and are compared with the recent observational upper limits. To the extent that the universe has not been reionized after recombination, the observed upper limits of the temperature anisotropies on small angular scales rule out the cosmological models without nonbaryonic dark matter. In turn, this would provide strong support for (nonbaryonic) dark matter, independently of the results of standard primordial nucleosynthesis. Reionization after recombination, if any, might allow an isocurvature baryonic universe as a viable model, only when the initial density power spectrum was very steep. 64 refs.

A Hydro-Dynamical Model for Gravity

Abstract: A hydro-dynamical model for gravity by using an analogy with the attraction of spherical sources in incompressible fluids is proposed. Information regarding a photon-like particle called graviton is taken using an author's previous paper (6). The substance and radiation interaction due to emission of gravitons takes place via an energy field made of the emitted gravitons and filling the entire universe. The energy distribution is considered uniform at the universe scale. A consequence of the proposed model is the increasing of the universal "constant" of gravity, as a function of the age of universe.

The dynamical evolution of 3-space in a higher dimensional steady state universe

Abstract: We investigate a class of cosmological solutions of Einstein’s field equations in higher dimensions with a cosmological constant and an ideal fluid matter distribution as a source We discuss the dynamical evolution of the universe subject to two constraints that (i) the total volume scale factor of the universe is constant and (ii) the effective energy density is constant We obtain various interesting new dynamics for the external space that yield a time varying deceleration parameter including oscillating cases when the flat/curved external and curved/flat internal spaces are considered We also comment on how the universe would be conceived by an observer in four dimensions who is unaware of the extra dimensions