Deceleration parameter

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

Interaction between Generalized Varying Chaplygin gas and Tachyonic Fluid

Abstract: We consider a mixture of varying Generalized Chaplyagin gas [1] interacting with a Tachyonic fluid in framework of GR. We suppose, that a Tachyonic fluid and Generalized Chaplyagin gas was separated somehow from Darkness of the Universe. Remaining darkness will be described by $\omega_{X}$ and we will have not any other information. We also suppose, that varying Generalized Chaplyagin gas under consideration was appeared due to interaction between remaining Darkness and Generalized Chaplyagin gas. At the same time we assume, that our Tachonic fluid does not fell remaining Darkness. In this letter we investigate graphically the potential $V(\phi)$ of the Tachyonic fluid and $\omega_{\small{tot}}$ of the mixture. Interaction between components taken to be sign-changeable, occurring thanks to imposing of deceleration parameter into expression of interaction term [2],[3].

A divergence free parametrization of deceleration parameter for scalar field dark energy

Abstract: In this paper, we have considered a spatially flat FRW universe filled with pressureless matter and dark energy. We have considered a phenomenological parametrization of the deceleration parameter $q(z)$ and from this we have reconstructed the equation of state for dark energy $\omega_{\phi}(z)$. This divergence free parametrization of the deceleration parameter is inspired from one of the most popular parametrization of the dark energy equation of state given by Barboza and Alcaniz. Using the combination of datasets (SN Ia $+$ Hubble $+$ BAO/CMB), we have constrained the transition redshift $z_{t}$ (at which the universe switches from a decelerating to an accelerating phase) and have found the best fit value of $z_{t}$. We have also compared the reconstructed results of $q(z)$ and $\omega_{\phi}(z)$ and have found that the results are compatible with a $\Lambda$CDM universe if we consider SN Ia $+$ Hubble data but inclusion of BAO/CMB data makes $q(z)$ and $\omega_{\phi}(z)$ incompatible with $\Lambda$CDM model. The potential term for the present toy model is found to be functionally similar to a Higgs potential.

A comprehensive investigation on the slowing down of cosmic acceleration

Abstract: Shafieloo ea al. firstly proposed the possibility that the current cosmic acceleration (CA) is slowing down. However, this is rather counterintuitive because a slowing down CA cannot be accommodated in most mainstream cosmological models. In this work, by exploring the evolutionary trajectories of dark energy equation of state w(z) and deceleration parameter q(z), we present a comprehensive investigation on the slowing down of CA from both the theoretical and the observational sides. For the theoretical side, we study the impact of different w(z) by using six parametrization models, and then discuss the effects of spatial curvature. For the observational side, we investigate the effects of different type Ia supernovae (SNe Ia), different baryon acoustic oscillation (BAO), and different cosmic microwave background (CMB) data, respectively. We find that (1) The evolution of CA are insensitive to the specific form of w(z); in contrast, a non-flat Universe more favors a slowing down CA than a flat Universe. (2) SNLS3 SNe Ia datasets favor a slowing down CA at 1 confidence level, while JLA SNe Ia samples prefer an eternal CA; in contrast, the effects of different BAO data are negligible. (3) Compared with CMB distance prior data, full CMB data more favor a slowing down CA. (4) Due to the low significance, the slowing down of CA is still a theoretical possibility that cannot be confirmed by the current observations. Subject headings: Cosmology: dark energy, observations, cosmological parameters

An Exact Bianchi Type-I Cosmological Model in Lyra's Manifold

Abstract: A spatially homogeneous and anisotropic Bianchi type-I space–time has been studied within the framework of Lyra's geometry. Exact solutions of the Einstein's field equations have been obtained with a time dependent gauge function by using a special law of variation for Hubble's parameter that yields a constant value of deceleration parameter. It has been found that the solutions generalize the solutions obtained by Rahaman et al. [Astrophys. Space Sci.299, 211 (2005)] and are consistent with the recent observations of type Ia supernovae. A detailed study of physical and kinematical properties of the model has been carried out.

Statefinder diagnostic and constraints on the Palatini f(R) gravity theories

Abstract: We focus on a series of f(R) gravity theories in Palatini formalism to investigate the probabilities of producing late-time acceleration for the flat Friedmann-Robertson-Walker (FRW) universe. We apply a statefinder diagnostic to these cosmological models for chosen series of parameters to see if they can be distinguished from one another. The diagnostic involves the statefinder pair {r, s}, where r is derived from the scale factor a and its higher derivatives with respect to the cosmic time t, and s is expressed by r and the deceleration parameter q. In conclusion, we find that although two types of f(R) theories: (i) f(R) = R + αRm – βR −n and (ii) f(R) = R + α ln R – β can lead to late-time acceleration, their evolutionary trajectories in the r – s and r – q planes reveal different evolutionary properties, which certainly justify the merits of the statefinder diagnostic. Additionally, we utilize the observational Hubble parameter data (OHD) to constrain these models of f(R) gravity. As a result, except for m = n = 1/2 in case (i), α = 0 in case (i) and case (ii) allow the ΛCDM model to exist in the 1σ confidence region. After applying the statefinder diagnostic to the best-fit models, we find that all the best-fit models are capable of going through the deceleration/acceleration transition stage with a late-time acceleration epoch, and all these models turn to the de Sitter point ({r, s} = {1, 0}) in the future. Also, the evolutionary differences between these models are distinct, especially in the r – s plane, which makes the statefinder diagnostic more reliable in discriminating cosmological models.