Deceleration parameter

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

Will There Be Future Deceleration? A Study of Particle Creation Mechanism in Nonequilibrium Thermodynamics

Abstract: The paper deals with nonequilibrium thermodynamics based on adiabatic particle creation mechanism with the motivation of considering it as an alternative choice to explain the recent observed accelerating phase of the universe. Using Friedmann’s equations, it is shown that the deceleration parameter () can be obtained from the knowledge of the particle production rate (). Motivated by thermodynamical point of view, cosmological solutions are evaluated for the particle creation rates in three cosmic phases, namely, inflation, matter dominated era, and present late time acceleration. The deceleration parameter () is expressed as a function of the redshift parameter (), and its variation is presented graphically. Also, statefinder analysis has been presented graphically in three different phases of the universe. Finally, two noninteracting fluids with different particle creation rates are considered as cosmic substratum, and deceleration parameter () is evaluated. Whether more than one transition of is possible or not is examined by graphical representations.

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 because of the geometry of the universe, as well as because of 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 q0, the density parameter Ω0, 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 β0 ≡ Ω00.6/b from a galaxy redshift survey on the basis of a conventional estimator for β0, which neglects both the geometrical distortion effect and the time evolution of the parameter β(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 definitely dominate the expected statistical error for future surveys.

New agegraphic dark energy model in Brans-Dicke theory with logarithmic form of scalar field

Abstract: In this paper, the cosmological evolution of new agegraphic dark energy (NADE) model is analyzed in Brans-Dicke theory within the framework of Friedmann-Robertson-Walker Universe. The power-law assumption on Brans-Dicke scalar field is reconsidered by assuming the logarithmic form. We derive the equation of state parameter \(w_{D}\) and deceleration parameter \(q\) of NADE model. It is observed that \(w_{D}\rightarrow -1\) when \(a\rightarrow \infty \), i.e., the NADE mimics cosmological constant in the late time evolution. Indeed, due to the assumption of logarithmic form of Brans-Dicke scalar field the NADE in Brans-Dicke theory behaves like NADE in general relativity in the late time evolution. The NADE model shows a phase transition from matter dominated phase in early time to accelerated phase in late time. We further extend NADE model by including the interaction between dark matter and NADE. In this case, \(w_{D}\) definitely crosses the phantom divide line (\(w_{D}=-1\)) in the late time evolution. The phase transition from matter dominated to NADE dominated phase may be achieved at early stage in interacting model. Further, we show that the interacting NADE model resolves the cosmic coincidence problem as the energy density ratio may evolve sufficiently slow at present.

A new class of LRS Bianchi type-II dark energy models with variable EoS parameter

Abstract: A new class of dark energy models in a Locally Rotationally Symmetric Bianchi type-II (LRS B-II) space-time with variable equation of state (EoS) parameter and constant deceleration parameter have been investigated in the present paper. The Einstein’s field equations have been solved by applying a variation law for generalized Hubble’s parameter given by Berman: Nuovo Cimento 74:182 (1983) which generates two types of solutions for the average scale factor, one is of power-law type and other is of the exponential-law form. Using these two forms, Einstein’s field equations are solved separately that correspond to expanding singular and non-singular models of the universe respectively. The dark energy EoS parameter ω is found to be time dependent and its existing range for both models is in good agreement with the three recent observations of (i) SNe Ia data (Knop et al.: Astrophys. J. 598:102 (2003)), (ii) SNe Ia data collaborated with CMBR anisotropy and galaxy clustering statistics (Tegmark et al.: Astrophys. J. 606:702 (2004)) and latest (iii) a combination of cosmological datasets coming from CMB anisotropies, luminosity distances of high redshift type Ia supernovae and galaxy clustering (Hinshaw et al.: Astrophys. J. Suppl. 180:225 (2009); Komatsu et al. Astrophys. J. Suppl. 180:330 (2009)). The cosmological constant Λ is found to be a positive decreasing function of time and it approaches a small positive value at late time (i.e. the present epoch) which is corroborated by results from recent supernovae Ia observations. The physical and geometric behaviour of the universe have also been discussed in detail.

Anisotropic Viscous Fluid Cosmological Models from Deceleration to Acceleration in String Cosmology

Abstract: In the present study, anisotropic locally rotationally symmetric (LRS) Bianchi type II models representing massive strings have been presented with variable mean deceleration parameter. The field equations in scalar-tensor theory with energy momentum tensor proposed by Letelier (Phys. Rev. D 28: 2414, 1983), have been solved for the bulk viscous fluid and perfect fluid under the following physically relevant assumptions: (a) scale factor varies with time as $a(t) = (\sinh(\alpha t))^{\frac{1}{n}}$ , (b) Expansion (θ) in the model is proportional to shear (σ), (c) p=γρ, where γ (0≤γ≤1) is a constant, (d) ξ(t)=ξ 0 ρ η . It has been observed that the presented universe has a phase transition from the early decelerating phase to the accelerating phase at present epoch which is in good agreement with the recent astronomical observations. Moreover, some physical and geometric properties of the models have been discussed in detail.