Deceleration parameter

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

Cosmological Constraint and Analysis on Holographic Dark Energy Model Characterized by the Conformal-age-like Length

Abstract: We present a best-fit analysis on the single-parameter holographic dark energy model characterized by the conformal-age-like length, $L=\frac{1}{a^4(t)}\int_0^tdt' a^3(t') $. Based on the Union2 compilation of 557 supernova Ia data, the baryon acoustic oscillation results from the SDSS DR7 and the cosmic microwave background radiation data from the WMAP7, we show that the model gives the minimal $\chi^2_{min}=546.273$, which is comparable to $\chi^2_{\Lambda{\rm CDM}}=544.616$ for the $\Lambda$CDM model. The single parameter $d$ concerned in the model is found to be $d=0.232\pm 0.006\pm 0.009$. Since the fractional density of dark energy $\Omega_{de}\sim d^2a^2$ at $a \ll 1$, the fraction of dark energy is naturally negligible in the early universe, $\Omega_{de} \ll 1$ at $a \ll 1$. The resulting constraints on the present fractional energy density of matter and the equation of state are $\Omega_{m0}=0.286^{+0.019}_{-0.018}^{+0.032}_{-0.028}$ and $w_{de0}=-1.240^{+0.027}_{-0.027}^{+0.045}_{-0.044}$ respectively. The model leads to a slightly larger fraction of matter comparing to the $\Lambda$CDM model. We also provide a systematic analysis on the cosmic evolutions of the fractional energy density of dark energy, the equation of state of dark energy, the deceleration parameter and the statefinder. It is noticed that the equation of state crosses from $w_{de}>-1$ to $w_{de} 0$) to accelerated expansion ($q<0$) recently, and the statefinder may serve as a sensitive diagnostic to distinguish the CHDE model with the $\Lambda$CDM model.

Constraints on transition redshift and deceleration parameter from recent observations

Abstract: In this paper, the 1σ confidence level of transition redshift and present deceleration parameter are studied using modified Chaplygin gas (MCG) model from recent observations: the 182 Gold SNe Ia, three-year WMAP, SDSS baryon acoustic peak and X-ray gas mass fraction in clusters. Concretely, the best fit values of the transition redshift and present deceleration parameter with the 1σ confidence level are $z_{T}=0.45_{-0.09}^{+0.19}$ and $q_{0}=-0.64^{+0.15}_{-0.15}$, which indicate the best fit values of zT and q0 for MCG case are surprisingly close to the central values given by Refs. 20 and 21. Furthermore, we plot the evolution of cosmological quantities from MCG model by using the best-fit parameters given by combining constraint, and compare them with ΛCDM model.

Cosmology: going beyond the big bang

Abstract: Forty years ago cosmology was the realm of a handful of astronomers and two numbers were the holy grail: the Hubble constant, which describes the expansion of the universe, and the deceleration parameter, which describes how this expansion is slowing down due to gravity. Today, cosmology is an exciting area of research that attracts scientists ranging from astronomers and astrophysicists to experimental particle physicists and string theorists. The Hubble constant and the deceleration parameter have still not been measured, although they may be soon. The new holy grail, however, is to show that all structure in the universe evolved from quantum fluctuations.

LRS Bianchi Type-I Bulk Viscous Cosmological Models in f ( R, T ) Gravity

Abstract: We have studied the locally rotationally symmetric (LRS) Bianchi type-I cosmological model in f (R, T) gravity (R is the Ricci scalar and T is the trace of the stress energy tensor) with bulk viscous fluid as matter content. The model is constructed for the linear form f (R, T) = R + 2f (T). The exact solution of the field equations is obtained by using a time varying deceleration parameter q for a suitable choice of the function f (T). In this case, the bulk viscous pressure $$ \overline{\mathrm{p}} $$ is found to be negative and the energy density ρ is found to be positive. The obtained model is anisotropic, accelerating, and compatible with the results of astronomical observations. Also, some important features of physical parameters of this model have been discussed.

A dark energy model with variable eos parameter in self-creation theory of gravitation

Abstract: We have constructed LRS Bianchi type I dark energy models with variable equation of state (EoS) parameter in Barber’s second self creation theory. We found the equation of state for dark energy is time independent and its existing range for derived models is in good agreement with the recent observations of SNe Ia data. In order to obtain a determinate solution of the field equations we consider the special law of variation of Hubble’s parameter (Berman in Nuovo Cimento B 74, 182, 1983) which yields a cosmological model with negative deceleration parameter. Some physical and geometrical aspects of the models are also discussed.