Deceleration parameter

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

Testing Lambda and the Limits of Cosmography with the Union2.1 Supernova Compilation

Abstract: We present a cosmographic study designed to test the simplest type of accelerating cosmology: a flat universe with matter and a cosmological constant ($\Lambda$). Hubble series expansions are fit to the SCP Union2.1 supernova data set to estimate the Hubble Constant ($H_{0}$), the deceleration parameter ($q_{0}$), and the jerk parameter ($j_{0}$). Flat $\Lambda$CDM models always require $j_{0} = 1$, providing a single-parameter test of the entire paradigm. Because of convergence issues for $z \gtrsim 1$, we focus on expansions using the newer redshift variable $y$, and to estimate the effects of "model-building uncertainties" -- the dependence of the output results upon the fitting function and parameters used -- we perform fits using five different distance indicator functions, and four different polynomial orders. We find that one cannot yet use the supernova data to reliably obtain more than four cosmological parameters, and that cosmographic estimates of $j_{0}$ remain dominated by model-building uncertainties, in conjunction with statistical and other error sources. While $j_{0} = 1$ remains consistent with Union2.1, the most restrictive bound that we can place is $j_{0} \sim [-7.6,8.5]$. To test the future prospects of cosmography with new standard candle data, ensembles of mock supernova data sets are created, and it is found that the best way to reduce model-building uncertainties on lower-order Hubble parameters (such as $\{H_{0}, q_{0}, j_{0} \}$) is by limiting the redshift range of the data. Thus more and better $z \lesssim 1$ data, not higher-redshift data, is needed to sharpen cosmographic tests of flat $\Lambda$CDM.

Interacting Tsallis holographic dark energy: Cosmic behaviour, statefinder analysis and ωD − ω' D pair in the non- flat universe

Abstract: The paper explores the interacting Tsallis holographic dark energy (THDE) model in a non-flat universe following an infrared cutoff as the apparent horizon. The equation of state (EoS) and the deceleration parameter of THDE model are determined to understand the cosmological evolution for interacting THDE model in the nonflat universe. By applying the statefinder $(r, s)$ parameter-pairs diagnostic and $\omega_D-\omega'_D$ pair dynamical analysis for the derived THDE model, we plot the evolutionary trajectories for different cases of Tsallis parameter $\delta$ and interaction term $b^{2}$ and also, for spatial curvature $\Omega_{k0}= 0, -0.0012$ and $0.0026$ corresponding to flat, open and closed universes, respectively, in the framework of Planck 2018 base cosmology results VI-LCDM observational data.

Accelerating Dark Energy Cosmological Model in Two Fluid with Hybrid Scale Factor

Abstract: In this paper, we have investigated the anisotropic behavior of the accelerating universe in Bianchi V space time in the frame work of General Relativity (GR). The matter field we have considered is of two non interacting fluids i.e. the usual string fluid and dark energy (DE) fluid. In order to represent the pressure anisotropy, the skewness parameters are introduced along three different spatial directions. To achieve a physically realistic solutions to the field equations, we have considered a scale factor, known as hybrid scale factor, which is generated by a time varying deceleration parameter. This simulates a cosmic transition from early deceleration to late time acceleration. It is observed that the string fluid dominates the universe at early deceleration phase but does not affect nature of cosmic dynamics substantially at late phase where as, the DE fluid dominates the universe in present time, which is in accordance with the observations results. Hence, we analysed here the role of two fluids in the transitional phases of universe with respect to time which depicts the reason behind the cosmic expansion and DE. The role of DE with variable equation of state parameter (EoS), skewness parameters also discussed along with physical and geometrical properties.

Constraints on modified Chaplygin gas from large scale structure

Abstract: We study cosmological models with modified Chaplygin gas (MCG) to determine observational constraints on its EoS parameters using the background and the growth tests data. The background test data consists of $H(z)-z$ data, Baryonic Acoustic Oscillations peak parameter, CMB shift parameter, SN Ia data and the growth test data consists of the linear growth function for the large scale structures of the universe are considered to study MCG in favor of dark energy. For a given range of redshift, the Wiggle-Z measurements and rms mass fluctuations from Ly- $\alpha $ data, employed for analyzing cosmological models numerically to constrain the MCG parameters. The Wang-Steinhardt ansatz for the growth index ( $\gamma $ ) and growth function ( $f$ ) are also considered for numerical analysis. The best-fit values of EoS parameters determined here are used to study the variation of $f$ , growth index ( $\gamma $ ), EoS parameter, squared sound speed and deceleration parameter with redshift. The constraints on the MCG parameters found here are compared with that of GCG (generalized Chaplygin gas) model for viable cosmology. Cosmologies with MCG satisfactorily describe late acceleration followed by a matter dominated phase. The range of values of EoS parameters, the associated parameters ( $f$ , $\gamma $ , $\omega $ , $\varOmega $ , $c^{2}_{s}$ , $q$ ) are also determined from observational data in order to understand the suitability of the MCG model.