Particle horizon

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

Holographic dark energy characterized by the total comoving horizon and insights into a cosmological constant and the coincidence problem

Abstract: The observed acceleration of the present Universe is shown to be well explained by the holographic dark energy characterized by the total comoving horizon of the Universe (eta HDE). It is of interest to notice that the very large primordial part of the comoving horizon generated by the inflation of the early Universe makes the eta HDE behave like a cosmological constant. As a consequence, both the fine-tuning problem and the coincidence problem can reasonably be understood with the inflationary universe and holo-graphical principle. We present a systematic analysis and obtain a consistent cosmological constraint on the eta HDE model based on the recent cosmological observations. It is found that the eta HDE model gives the best-fit result Omega(m0) = 0: 270 (Omega(de0) = 0: 730) and the minimal chi(2)(min) = 542: 915 which is compatible with chi(2)(ACDM) = 542: 919 for the ACDM model.

Is the Cosmic Transparency Spatially Homogeneous

Abstract: We study the constraints on the cosmic opacity using the latest BAO and Union2 SNIa data in this paper and find that the best fit values seem to indicate that an opaque universe is preferred in redshift regions $0.20-0.35$, $0.35-0.44$ and $0.60-0.73$, whereas, a transparent universe is favored in redshift regions $0.106-0.20$, $0.44-0.57$and $0.57-0.60$. However, our result is still consistent with a transparent universe at the 1$\sigma$ confidence level, even though the best-fit cosmic opacity oscillates between zero and some nonzero values as the redshift varies.

Cosmological evolution of cosmic strings with time-dependent tension

Abstract: We discuss the cosmological evolution of cosmic strings with time-dependent tension. We show that, in the case that the tension changes as a power of time, the cosmic string network obeys the scaling solution: the characteristic scale of the string network grows with the time. But due to the time dependence of the tension, the ratio of the energy density of infinite strings to that of the background universe is not necessarily constant.

Emergent Universe in Einstein-Gauss-Bonnet Theory

Abstract: In this work, Emergent Universe scenario has been developed in Einstein-Gauss-Bonnet (EGB) theory. The universe is chosen as homogeneous and isotropic FRW model and the matter in the universe has two components—the first one is a perfect fluid with barotropic equation of state p=ωρ (ω, a constant) and the other component is a real or phantom (or tachyonic) scalar field. Various possibilities for the existence of emergent scenario has been discussed and the results are compared with those in Einstein gravity.

Cosmological horizon entropy and generalized second law for flat Friedmann universe

Abstract: We investigate the generalized second law (GSL) and the constraints imposed by it for two types of Friedmann universes. The first one is the Friedmann universe with radiation and a positive cosmological constant, and the second one consists of non-relativistic matter and a positive cosmological constant. The time evolution of the event horizon entropy and the entropy of the contents within the horizon are studied by obtaining the Hubble parameter. It is shown that the GSL constrains the temperature of both the radiation and matter of the Friedmann universe. It is also shown that, even though the net entropy of the radiation (or matter) is decreasing at sufficiently large times as the universe expands, it exhibits an increase during the early times when the universe is decelerating. That is, the entropy of the radiation within the comoving volume is decreasing only when the universe is undergoing an accelerated expansion.