LRS Bianchi I model with constant expansion rate in $f(R,T)$ gravity

Abstract

Locally-rotationally-symmetric Bianchi-I space-time model is studied with constant Hubble parameter in $f(R,T)=R+2\lambda T$ gravity. Although a single (primary) matter source is considered, an additional matter source appears due to the coupling between matter and $f(R,T)$ gravity. The constraints are obtained for a realistic cosmological scenario. The solutions are also extended to the case of a scalar field (normal or phantom) model, and it is found that the model is consistent with a phantom scalar field only. The coupled matter also acts as phantom matter. The study shows that if one expects an accelerating universe from an anisotropic model, then the solutions become physically relevant only at late times when the universe enters into an accelerated phase. Placing some observational bounds on the present equation of state of dark energy, $\omega_{0}$, the behavior of $\omega(z)$ is depicted, which shows that the phantom field starts dominating very recently, somewhere between $0.2\lesssim z\lesssim0.5$. The geometrical behavior of the model remains identical to the one in general relativity.