Deceleration parameter

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

Two-fluid atmosphere from decelerating to accelerating FRW dark energy models

Abstract: The evolution of the dark energy parameter within the scope of a spatially homogeneous and isotropic Friedmann-Robertson-Walker (FRW) model filled with perfect fluid and dark energy components is studied by generalizing the recent results (Amirhashchi et al. in Int. J. Theor. Phys. 50: 3529, 2011b). The two sources are claimed to interact minimally so that their energy momentum tensors are conserved separately. The conception of time-dependent deceleration parameter (DP) with some suitable assumption yields an average scale factor $a = [\sinh (\alpha t)]^{\frac{1}{n}}$, with $\alpha$ and $n$ being positive arbitrary constants. For $0 1$, the models of universe exhibit phase transition from early decelerating phase to present accelerating phase which is supported with the results from recent astrophysical observations. It is observed that the transition red shift ($z_{t}$) for our derived model with $q_{0} = -0.73$ is $\cong 0.32$. This is in good agreement with the cosmological observations in the literature. Some physical and geometric properties of the model along with physical acceptability of cosmological solutions have been discussed in detail.

Probing the course of cosmic expansion with a combination of observational data

Abstract: We study the cosmic expansion history by reconstructing the deceleration parameter $q(z)$ from the SDSS-II type Ia supernova sample (SNIa) with two different light curve fits (MLCS2k2 and SALT-II), the baryon acoustic oscillation (BAO) distance ratio, the cosmic microwave background (CMB) shift parameter, and the lookback time-redshift (LT) from the age of old passive galaxies. Three parametrization forms for the equation of state of dark energy (CPL, JBP, and UIS) are considered. Our results show that, for the CPL and the UIS forms, MLCS2k2 SDSS-II SNIa+BAO+CMB and MLCS2k2 SDSS-II SNIa+BAO+CMB+LT favor a currently slowing-down cosmic acceleration, but this does not occur for all other cases, where an increasing cosmic acceleration is still favored. Thus, the reconstructed evolutionary behaviors of dark energy and the course of the cosmic acceleration are highly dependent both on the light curve fitting method for the SNIa and the parametrization form for the equation of state of dark energy.

The general class of Bianchi cosmological models in f(R, T) gravity with dark energy in viscous cosmology

Abstract: The general class of Bianchi cosmological models in f(R, T) gravity with dark energy in the form of standard and modified Chaplygin gas and bulk viscosity have been considered. We have discussed three types of average scale factor by using a special law for deceleration parameter which is linear in time with negative slope. The model describes an accelerating universe for large value of time t, wherein the effective negative pressure induced by Chaplygin gas and bulk viscous pressure are driving the acceleration.

Cosmological redshift distortion: deceleration, bias and density parameters from future redshift surveys of galaxies

Abstract: The observed two-point correlation functions of galaxies in redshift space become anisotropic due to the geometry of the universe as well as due to the presence of the peculiar velocity field. On the basis of linear perturbation theory, we expand the induced anisotropies of the correlation functions with respect to the redshift $z$, and obtain analytic formulae to infer the deceleration parameter $q_0$, the density parameter $\Omega_0$ and the derivative of the bias parameter $d\ln b/dz$ at $z=0$ in terms of the observable statistical quantities. The present method does not require any assumption of the shape and amplitude of the underlying fluctuation spectrum, and thus can be applied to future redshift surveys of galaxies including the Sloan Digital Sky Survey. We also evaluate quantitatively the systematic error in estimating the value of $\beta_0 \equiv \Omega_0^{0.6}/b$ from a galaxy redshift survey on the basis of a conventional estimator for $\beta_0$ which neglects both the geometrical distortion effect and the time evolution of the parameter $\beta(z)$. If the magnitude limit of the survey is as faint as 18.5 (in B-band) as in the case of the Sloan Digital Sky Survey, the systematic error ranges between -20% and 10% depending on the cosmological parameters. Although such systematic errors are smaller than the statistical errors in the current surveys, they will dominate the expected statistical error for future surveys.

Bianchi type v cosmological models with perfect fluid and heat conduction in lyra's geometry

Abstract: The field equations within the framework of Lyra's geometry with a time-dependent displacement vector field for a Bianchi type-V space–time filled with a perfect fluid and heat flow are presented. Two different classes of physically viable solutions are obtained by using a special law of variation for the generalized mean Hubble's parameter which correspond to singular and nonsingular models with constant deceleration parameter. These models are found to be consistent with the observations on the present day universe. Some thermodynamical relations are studied. The physical and kinematical behaviors of the models are also discussed.