Bianchi type-III models with anisotropic dark energy in Brans–Dicke–Rastall theory

Abstract

In this paper, we consider the Bianchi type-III metric (which is a spatially homogeneous and anisotropic) in the framework of a newly proposed Brans–Dicke–Rastall theory of gravitation by Caramês et al. (Eur. Phys. J. C 74:3145, 2014). In this scenario, we obtain the generalized form of the anisotropy parameter of the expansion, the dynamically anisotropic equation of state parameter, and a dynamical energy density in the presence of a single diagonal imperfect fluid. By assuming the anisotropy of the fluid, and exponential and power-law volumetric expansions, we find the exact solutions of the Brans–Dicke–Rastall field equations. We examine the isotropy of the fluid, of space, and of the expansion of the universe. It is observed that the universe can approach the isotropy monotonically even in the presence of an anisotropic fluid. We also note that the strong anisotropy observed in RG, respectively, is diminished considerably in the Rastall theory and Brans–Dicke–Rastall theory because of the influence of the parameters $\lambda_{\mathrm{Ras}}$ and $\omega_{\mathrm{BD}}$.