Deceleration parameter

About: Deceleration parameter is a research topic. Over the lifetime, 1776 publications have been published within this topic receiving 89440 citations.

Statefinder and Om Diagnostics for Interacting New Holographic Dark Energy Model and Generalized Second Law of Thermodynamics

Abstract: In this work, we have considered that the flat FRW universe is filled with the mixture of dark matter and the new holographic dark energy. If there is an interaction, we have investigated the natures of deceleration parameter, statefinder and Om diagnostics. We have examined the validity of the first and generalized second laws of thermodynamics under these interactions on the event as well as apparent horizon. It has been observed that the first law is violated on the event horizon. However, the generalized second law is valid throughout the evolution of the universe enveloped by the apparent horizon. When the event horizon is considered as the enveloping horizon, the generalized second law is found to break down excepting at late stage of the universe.

A new parametrization of dark energy equation of state leading to double exponential potential

Abstract: We show that a canonical scalar field with a phenomenological form of energy density or equivalently an equation of state parameter can provide the required transition from decelerated ($q>0$) to accelerated expansion ($q<0$) phase of the universe. We have used the latest Type Ia Supernova (SNIa) and Hubble parameter datasets to constrain the model parameters. It has been found that for each of these dataset, the transition in deceleration parameter $q$ takes place at the recent past ($z<1$). The future evolution of $q$ is also discussed in the context of the model under consideration. Furthermore, using those datasets, we have reconstructed $\omega_{\phi}(z)$, the equation of state parameter for the scalar field. The results show that the reconstructed forms of $q(z)$ and $\omega_{\phi}(z)$ do not differ much from the standard $\Lambda$CDM value at the current epoch. Finally, the functional form of the relevant potential $V(\phi)$ is derived by a parametric reconstruction from the observational dataset. The corresponding $V(\phi)$ comes out to be a double exponential potential which has a number of cosmological implications. Additionally, we have also studied the effect of this particular scalar field dark energy sector on the evolution of matter over-densities and compared it with the $\Lambda$CDM model.

Universe evolution in a 5D ricci-flat cosmology

Abstract: We use Wetterich's parametrization equation of state (EOS) of dark energy to a 5D Ricci-flat cosmological solution and we assume that the universe contains three major components: matter, radiation and dark energy. By using the relation between the scale factor and the redshift z, we show that the two arbitrary functions contained in the 5D solution could be solved out analytically in terms of the variable z. Thus the whole 5D solution could be constructed uniquely if the current values of the three density parameters Ωm0, Ωr0, Ωx0, the EOS w0, and the bending parameter b contained in the EOS are all known. Furthermore, we find that all the evolutions of the mass density Ωm, the radiation density Ωr, the dark energy density Ωx, and the deceleration parameter q depend on the bending parameter b sensitively. Therefore it is worthwhile to study observational constraints on the bending parameter b.

On the possible existence of cosmological cosmic rays. I. The framework for light-element and gamma-ray production.

Abstract: This paper examines the possibility of the existence of cosmological cosmic rays (CCR), in the framework of big-bang cosmology. The model assumes a total energy spectrum similar to that observed at Earth at high energies, a composition of protons and ..cap alpha..-particles only, with ..cap alpha../p=0.1. Following Stecker, the CCR are assumed to be born in a burst at some (high) redshift z/sub s/. Gamma-rays originate from ..pi../sup 0/ decay resulting from interactions of the high-energy part of the CCR, and light elements are produced via (p..cap alpha..)+(p..cap alpha..) reactions by the low-energy part, both of them by collisions with the ambient matter (of density corresponding to a deceleration parameter q/sub 0/).The 1--100 MeV ..gamma..-ray background spectrum and the lithium abundance are considered as observational constraints on the possible CCR flux intensity. To this end, a theoretical framework is set for simultaneous ..gamma..-ray and light-element production by solving a system of coupled time-dependent transport equations, taking ionization and expansion losses into account. The absolute lithium abundance is calculated by normalizing the CCR flux to the observed ..gamma..-ray background spectrum; numerical results will be given and discussed in a separate paper, as a function of q/sub 0/ and z/sub s/.