Late-time acceleration with a scalar field source: Observational constraints and statefinder diagnostics

Abstract

This article discusses a dark energy cosmological model in the standard theory of gravity -general relativity with a broad scalar field as a source. Exact solutions of Einstein's field equations are derived by considering a particular form of deceleration parameter q, which shows a smooth transition from decelerated to accelerated phase in the evolution of the universe. The external datasets such as Hubble (H(z)) datasets, Supernovae (SN) datasets, and Baryonic Acoustic Oscillation (BAO) datasets are used for constraining the model par parameters appearing in the functional form of q. The transition redshift is obtained at z t = 0.67 +0.26 −0.36 for the combined data set (H(z) + SN + BAO), where the model shows signature-flipping and is consistent with recent observations. Moreover, the present value of the deceleration parameter comes out to be q 0 = −0.50 +0.12 −0.11 and the jerk parameter j 0 = −0.98 +0.06 −0.02 (close to 1) for the combined datasets, which is compatible as per Planck2018 results. The analysis also constrains the omega value i.e., Ω m 0 ≤ 0.269 for the smooth evolution of the scalar field EoS parameter. It is seen that energy density is higher for the effective energy density of the matter field than energy density in the presence of a scalar field. The evolution of the physical and geometrical parameters is discussed in some details with the model parameters' numerical constrained values. Moreover, we have performed the state-finder analysis to investigate the nature of dark energy.

Cosmological aspects of $f(R,T)$ gravity in a simple model with a parametrization of $q$

“…Additionally, this article is an attempt to design a cosmic model by taking a suitable parametrization of the deceleration parameter, which was first considered in the paper [88] wherein two phenomena Big Rip and Big Bang of the Universe were discussed together with the cosmic evolution in the general theory of relativity. Later on, the same model is studied in the paper [94] where the authors found some observational constraints using some external datasets and also discussed the statefinder diagnostics. Here, in our study, we have taken the motivation from [88] and [94] and extended the study in f (R, T ) gravity wherein our main intention is to study the physical parameters (especially EoS ω) in f (R, T ) gravity with quadratic correction terms i.e.…”

“…Later on, the same model is studied in the paper [94] where the authors found some observational constraints using some external datasets and also discussed the statefinder diagnostics. Here, in our study, we have taken the motivation from [88] and [94] and extended the study in f (R, T ) gravity wherein our main intention is to study the physical parameters (especially EoS ω) in f (R, T ) gravity with quadratic correction terms i.e. f (R, T ) = R + αR 2 + 2λT .…”

“…1 of deceleration parameter, we can interpret the cosmological phase transition from early deceleration to present acceleration with the present value of the deceleration parameter q 0 < 0 and in the far future, the highly negative value of q indicates the super acceleration phase leading to a Big Rip singularity. Pacif et al [94] have discussed a model in general relativity with this same parametrization of q and constrained the model parameters with some external datasets (Hubble datasets, Supernovae datasets, and Baryonic Acoustic Oscillation datasets) involved in the model i.e., γ and β and they have found the values of these model parameters as γ = 0.44 +0.01 −0.01 and β = 1.09 +0.11 −0.11 for which q 0 = −0.50 +0.12 −0.11 and the phase transition occurs at z t = 0.67 +0.26 −0.36 . Since our discussed model is based on the same parametrization scheme q = (8γ 2 − 1) − 12γt + 3t 2 , we can use these constrained values of the model parameters for our subsequent analysis.…”

Bianchi type-V Transitioning model in Brans-Dicke theory with Observational Constraint

“…Thus we are at very large distance ( ∼ at infinite distance) from an event occurred in the beginning of the universe. The statefinder diagnostic is a valuable tool in current cosmology used to differentiate various dark energy models [100][101][102][103]. Different trajectories in the (r − s) (r − q) and (s − q) planes express the time evolution for various dark energy models.…”

Roles of Modified Chaplygin-Jacobi and Chaplygin-Abel Gases in FRW Universe

“…The cosmography is the study of scale factor by expanding it by Taylor series with respect to the cosmic time. The cosmographical parameter like jerk (J), snap (S), and lerk (L) parameters are [91][92][93][94]…”