Particle horizon

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

Bianchi—V string cosmological model and late time acceleration

Abstract: We have searched for the existence of the late time acceleration of the universe with string fluid as the source of matter in Bianchi—V space-time. To derive a deterministic solution, we choose the scale factor to be an increasing function of time that yields a time dependent deceleration parameter, representing a model which generates a universe showing a transition from an early decelerating phase to a recent accelerating phase. The study reveals that strings dominate the early universe and eventually disappear from the universe for sufficiently large times, i.e. in the present epoch. This picture is consistent with current astronomical observations. The physical behavior of the universe is discussed in detail.

First Light in the Universe

Abstract: First Light.- Cosmological Feedbacks from the First Stars.- Observations of the High Redshift Universe.

The evolution of our local cosmic domain: effective causal limits

Abstract: The causal limit usually considered in cosmology is the particle horizon, delimiting the possibilities of causal connection in the expanding Universe. However, it is not a realistic indicator of the effective local limits of important interactions in space–time. We consider here the matter horizon for the Solar system, i.e. the comoving region which has significantly contributed matter to our local physical environment. This lies inside the effective domain of dependence, which (assuming the universe is dominated by dark matter along with baryonic matter and vacuum-energy-like dark energy) consists of those regions that have had a significant active physical influence on this environment through effects such as matter accretion and acoustic waves. It is not determined by the velocity of light c, but by the flow of matter perturbations along their world lines and associated gravitational effects. We emphasize how small a region the perturbations which became our Galaxy occupied, relative to the observable universe – even relative to the smallest scale perturbations detectable in the cosmic microwave background radiation. Finally, looking to the future of our local cosmic domain, we suggest simple dynamical criteria for determining the present domain of influence and the future matter horizon. The former is the radial distance at which our local region is just now separating from the cosmic expansion. The latter represents the limits of growth of the matter horizon in the far future.

On the Thermodynamics of Dark Energy

Abstract: Recent astronomical observations suggest that the bulk of energy in the Universe is repulsive and appears like a dark energy component (which accounts for ~2/3 of the energy content of the Universe) with negative pressure (ω ≡ px/ρx < 0). In this work, we discuss the thermodynamic behavior by considering three different parametrizations, describing the dark energy component: (1) Model 1: ; (2) Model 2: ω(z) = ω0 + ω2 z; (3) Model 3: ω(z) = ω0 - ω3ln(1 + z). It is found that its energy and temperature grow during the evolution of the Universe since work is done on the system. The case of phantom energy (ω < -1), however, seems to be physically meaningless because its entropy is negative. Our analysis also implies that the ultimate fate of the Universe may be considerably modified. Actually, the future of the Universe depends on the kind of parametrization. For Models 1 and 3, the Universe will becoming increasingly hot, while for Model 2 it cools during evolution.