Anisotropic models with generalized hybrid expansion in Brans–Dicke theory of gravity

The hybrid expansion law (HEL) for average scale factor that yields power-law and exponential-law cosmologies is considered in spatially homogenous and anisotropic Bianchi type-I model in the context of Brans–Dicke (BD) Theory of gravitation. The solutions of the field equations have been calculated by assuming the power-law expression between the average scale factor [Formula: see text] and scalar field ([Formula: see text]). We studied both interacting and non-interacting forms of dark energy and dark matter and obtained respective solutions. The energy density [Formula: see text] decreases with time while energy densities [Formula: see text] increases with time. In both the cases, the physical acceptability and stability of the models are also studied. The coincidence problem in [Formula: see text]CDM model can be ruled out with proper choice of coupling between dark matter (DM) and dark energy (DE). We also discussed the physical behaviors of the derived models with the current observations applied to late-time acceleration and beginning of the universe. In this model, it is observed that our HEL Bianchi type I universe is highly anisotropic in the beginning of universe and becomes isotropic and overlaps with flat [Formula: see text]CDM model at late times.

Bianchi type–I Model with Time Varying Λ and G: The Generalized Solution

In this paper, we have investigated the homogeneous and anisotropic Bianchi type–I cosmological model with a time-varying Newtonian and cosmological constant. We have analytically solved Einstein’s field equations (EFEs) in the presence of a stiff-perfect fluid. We show that the analytical solution for the average scale factor for the generalized Friedman equation involves the hyper-geometric function. We have studied the physical and kinematical quantities of the model, and it is found that the universe becomes isotropic at late times.

Aspects of inflation in spatially homogeneous and anisotropic Bianchi Type I spacetime with exponential potential

The inflationary scenario in spatially homogeneous and anisotropic Bianchi Type I spacetime with exponential potential [Formula: see text], [Formula: see text] and average scale factor (R) is considered as [Formula: see text] is discussed. The model isotropizes in special case and asymptotically. The spatial volume increases with time representing inflationary scenario and the expansion continues for long enough, thus solving the horizon problem. The model represents decelerating and accelerating phases of universe in special case. Also, the model is singularity free at t = 0. In special case, i.e. when constants b = 0, k = 0, then the model leads to FLRW model for which we have the average scale factor [Formula: see text], [Formula: see text] and deceleration parameter [Formula: see text]. This paper gives the answer why anisotropic and homogeneous Bianchi Type I spacetime is considered than FRW model to discuss inflationary scenario.

Bianchi type-III holographic dark energy model with quintessence

In this study, we investigate an anisotropic Bianchi type-[Formula: see text] space-time in the presence of matter and holographic dark energy components within the framework of general relativity. We obtained the solution of the field equations by assuming (i) the expansion scalar [Formula: see text] in the model is proportional to shear scalar [Formula: see text], (ii) hybrid expansion law for average scale factor (keeping an eye on the recent scenario of accelerating nature of the universe). We develop cosmological parameters like deceleration and equation of state parameters. These parameters are plotted versus redshift [Formula: see text] for different values of power component of average scale factor [Formula: see text]. We observe that the equation of state varies in quintessence region ([Formula: see text]) and ultimately tends to [Formula: see text]CDM model ([Formula: see text]). The deceleration parameter exhibits a smooth transition from early decelerated epoch to present accelerated era. In addition, we establish the correspondence between our holographic dark energy model and quintessence scalar field. We also express the self-interacting potential [Formula: see text] and scalar field [Formula: see text] of quintessence model as functions of cosmic time [Formula: see text], which describes the accelerated expansion of the universe.

Bianchi type-VI0 modified holographic Ricci dark energy model in a scalar–tensor theory

In this paper, we consider Bianchi type-VI0 space–time filled with anisotropic modified holographic Ricci dark energy in a scalar–tensor theory proposed by Brans–Dicke (Phys. Rev. 124, 925 (1961)). The field equations in this scalar–tensor theory, have been solved for the following physically relevant assumptions: (i) the scalar field ([Formula: see text]) is proportional to average scale factor (a(t)), (ii) expansion scalar (θ) in the model is proportional to shear scalar (σ). It has been observed that the presented universe is in an accelerating phase at the present epoch, which is in good agreement with the recent astronomical observations. We have also discussed some other properties of the obtained model.

Bianchi type VI0 generalized ghost pilgrim dark energy model in Brans–Dicke theory of gravitation

In this paper, we solve Brans–Dicke (BD) theory (Phys. Rev. D, 24, 925) field equations for anisotropic Bianchi type VI0 space–time and discuss evolution of the expanding Universe. Here, we consider pressureless fluid and isotropic generalized ghost pilgrim dark energy as the source of matter and dark energy, respectively. To get the determinate solution of the field equations we have used (i) scalar expansion proportional to the shear scalar and (ii) scalar field (in BD theory) proportional to average scale factor of the model. Some physical and geometrical properties of the model are also discussed.

Bianchi types I and V bulk viscous fluid cosmological models in f(R, T) gravity theory

In this paper we present non-singular Bianchi types I and V cosmological models, in the presence of bulk viscous fluid and within the framework of f(R,T) gravity theory. Exact solutions to the field equations are obtained by choosing a particular form of the function f(R,T) and a special value for the average scale factor of the model, which corresponds to a time- dependent deceleration parameter. The cosmological models initially accelerate for a certain period of time and thereafter decelerate. The physical and kinematical properties of the models of the universe are discussed.