On a Bianchi type-I space-time with bulk viscosity in f(R,T) gravity

Abstract

In this paper, we present a spatially homogeneous and anisotropic Bianchi type-I cosmological model with a viscous bulk fluid in [Formula: see text] gravity where [Formula: see text] and [Formula: see text] are the Ricci scalar and trace of the energy-momentum tensor, respectively. The field equations are solved explicitly using the hybrid law of the scale factor, which is related to the average Hubble parameter and gives a time-varying deceleration parameter (DP). We found the deceleration parameter describing two phases in the universe, the early deceleration phase [Formula: see text] and the current acceleration phase [Formula: see text]. We have calculated some physical and geometric properties and their graphs, whether in terms of time or redshift. Note that for our model, the bulk viscous pressure [Formula: see text] is negative and the energy density [Formula: see text] is positive. The energy conditions and the [Formula: see text] analysis for our spatially homogeneous and anisotropic Bianchi type-I model are also discussed.

Holographic dark energy in Gauss-Bonnet gravity with Granda-Oliveros cut-off

“…the cosmic microwave background (CMB) anomalies from the results obtained by Planck [49]. Several researchers have studied homogeneous and anisotropic Bianchi models, such as the spatially homogeneous and anisotropic Bianchi type-I model, which is a direct generalization of the FLRW Universe with a scale factor in each spatial direction [38,39]. In this paper, motivated by the work [35], we study the holographic model of DE under f (G) gravity in the Bianchi type-I Universe, to find solutions of the field equations and some physical quantities, we will assume that the deceleration parameter (DP) varies with time.…”

“…The coincidence parameter (r) can be defined as the ratio between the HDE density (ρ Λ ) and the matter energy density (ρ m ), therefore for Eqs. (38) and (39) the coincidence parameter becomes…”

Flat LRW Universe in logarithmic symmetric teleparallel gravity with observational constraints

“…The principle of these theories is to replace the Ricci scalar R in the Einstein-Hilbert action S EH with a generalized function of R or other physical quantity. For example f (R) gravity, f (G) gravity, f (R, T ) gravity, etc [4][5][6][7][8][9][10]. The symmetric teleparallel gravity or f (Q) gravity is a modified theory of gravity suggested by J.…”

Anisotropic f(Q) gravity model with bulk viscosity

“…As a result, more attractive dynamical models based on the principle of modifying matter content of the Universe have appeared, such as quintessence, k-essence, Chapylygin gas, holographic dark energy, etc [8][9][10][11]. Recently, with researchers interested in the issue of cosmic acceleration, other alternatives have emerged called modified theories of gravity (MTG), which aim to modify the standard Einstein-Hilbert action and replace Ricci scalar curvature R with arbitrary functions of this scalar f (R) [12,13], or other physical quantities, such as f (R, T ) gravity (where R is the Ricci scalar and T is the trace of the energymomentum tensor) [14][15][16], f (G) gravity (where G is the Gauss-Bonnet invariant) [17][18][19], f (T ) gravity (where T is the torsion scalal) [20][21][22], f (Q) gravity (Q is the nonmetricity scalar), etc. In this work, we will examine a cosmological model in order to explain the cosmic acceleration in the framework of f (Q) symmetric teleparallel gravity proposed by Jiménez et al [23], where the non-metricity scalar Q is responsible for the gravitational interaction in this theory.…”