Deceleration parameter

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

On FRW Model in Conformal Teleparallel Gravity

Abstract: In this paper we use the conformal teleparallel gravity to study an isotropic and homogeneous Universe which is settled by the FRW metric. We solve the field equations and we obtain the behavior of some cosmological parameters such as scale factor, deceleration parameter and the energy density of the perfect fluid which is the matter field of our model. The field equations, that we called modified Friedmann equations, allow us to define a dark fluid, with dark energy density and dark pressure, responsible for the acceleration in the Universe.

Behaviour of f(T) dark energy model in fractal cosmology

Abstract: The f(T) modified gravity model is considered in the framework of fractal space-time. Assuming only the time has a fractal profile while the other spatial coordinates have their normal geometrical descriptions, the Hubble parameter, H, the dark energy density, $ \rho$ , the deceleration parameter, q, the pressure P, and state finder parameters r and s are reconstructed for our model. It is interesting to mention here that all the results are consistent with the recent present observations.

Time variable cosmological constant of holographic origin with interaction in Brans-Dicke theory

Abstract: Time variable cosmological constant (TVCC) of holographic origin with interaction in Brans–Dicke theory is discussed in this paper. We investigate some characters for this model, and show the evolutions of deceleration parameter and equation of state (EOS) for dark energy. It is shown that in this scenario an accelerating universe can be obtained and the evolution of EOS for dark energy can cross over the boundary of phantom divide. In addition, a geometrical diagnostic method, jerk parameter, is applied to this model to distinguish it with cosmological constant.

Recovering $\Lambda$CDM Model From a Cosmographic Study

Abstract: Using the mathematical definitions of deceleration and jerk parameters we obtain a general differential equation for squared Hubble parameter. For a constant jerk, this differential equation leads to an exact function for Hubble parameter. By the aid of this exact Hubble function we can exactly reconstruct any other cosmographic parameters. We also obtained a general function for transition redshift as well as spacetime curvature. Our derived functions clearly impose a lower limit on the jerk parameter which is $$j_{min}\ge -\,0.125$$. Moreover, we found that the jerk parameter indicates the geometry of the spacetime i.e any deviation from $$j=1$$ imply to a non-flat spacetime. In other word $$j e 1$$ refers to a dynamical, time varying, dark energy. From obtained Hubble function we recover the analogue of $$\Lambda $$CDM model. To constrain cosmographic parameters as well as transition redshift and spacetime curvature of the recovered $$\Lambda $$CDM model, we used Metropolis–Hasting algorithm to perform Monte Carlo Markov Chain analysis by using observational Hubble data obtained from cosmic chronometric technique, BAO data, Pantheon compilation of Supernovae type Ia, and their joint combination. The only free parameters are H, $$A(\Omega _{m})$$ and j. From joint analysis we obtained $$H_{0}=69.9\pm 1.7$$, $$A(\sim \Omega _{0m})=0.279^{+0.013}_{-0.017}$$, $$B(\sim \Omega _{0X})=0.721^{+0.017}_{-0.013}$$, $$j_{0}=1.038^{+0.061}_{-0.023}$$ and $$z_{t}=0.706^{+0.031}_{-0.034}$$.

Constraining a bulk viscous Bianchi type I dark energy dominated universe with recent observational data

Abstract: In this paper, we have investigated a bulk viscous universe with dominance of dark energy in Bianchi type I space-time and constrained its parameter with observational $H(z)$ data (OHD) and joint OHD and Pantheon compilation of SN Ia data. We constrain Hubble's constant ${H}_{0}=69.3{8}_{\ensuremath{-}1.54}^{+1.57}$ and ${H}_{0}=70.01{7}_{\ensuremath{-}1.60}^{+1.62}\text{ }\text{ }\mathrm{km}\text{ }{\mathrm{s}}^{\ensuremath{-}1}\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$ by bounding this model with OHD and joint OHD and Pantheon compilation of SN Ia data respectively. These estimated values of ${H}_{0}$ have $1.27\ensuremath{\sigma}$ and $1.69\ensuremath{\sigma}$ tension with its corresponding Planck collaboration value. We have constrained the best fit value of model parameter $\ensuremath{\zeta}$ as $\ensuremath{\zeta}=0.00002{7}_{\ensuremath{-}0.00052}^{+0.00052}$ and $\ensuremath{\zeta}=0.00003{3}_{\ensuremath{-}0.00296}^{+0.00296}$ respectively for the above observational datasets. We also have obtained a kinematic expression for deceleration parameter and constrained its present value ${q}_{0}=\ensuremath{-}0.58{2}_{\ensuremath{-}0.023}^{+0.021}$ and transition redshift ${z}_{t}=0.72{3}_{\ensuremath{-}0.16}^{+0.34}$. Furthermore, we observe that the derived model exhibits the properties of transitioning the universe and its present age is ${t}_{0}=14.0{4}_{\ensuremath{-}0.32}^{+0.33}\text{ }\text{ }\mathrm{Gyrs}$. The kinematics of the Om(z) parameter and the jerk parameter are also discussed and the analysis of these parameters shows a marginal departure of the derived model from the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model of the universe.