Inflationary Cosmology in a non-minimal $f(R,T)$ gravity theory using a $RT$ mixing term

Abstract

We investigate a class of inflationary models in modified gravity theories which contain a non-minimal coupling between gravity and a scalar field $\phi$ (inflaton) as $f(R,T)=R \bigl(1+\alpha+ \kappa^4 \beta T \bigr)+\kappa^2\gamma T $ where $\kappa^2=8\pi G$ where $G$ is the Newton's constant. We consider two inflaton potentials of the form (i) $V = V_0 \bigl(1 +\ln{\phi} \bigr)$ and (ii) $V_0\frac{\lambda \phi^p}{1+\lambda\phi^p}$. For a range of potential parameters, we explored the constraints on modified gravity parameters i.e. ($\alpha$, $\beta$ and $\gamma$) in three categories -- (i) $\beta \neq0$, $\alpha=\gamma=0$ (considering $R$ and $RT$ mixing terms), (ii) $\alpha=0$, $\gamma\neq0$, $\beta\neq 0$ ($RT$ mixing term along with $T$ and $R$ terms) and (iii) $\gamma=0$, $\alpha\neq0$, $\beta\neq0$ ($RT$ mixing term along with $R$ term) for the above two potentials. The inclusion of $RT$ mixing term provides the scalar spectral index $n_s$ up to $3\sigma$ limit of PLANCK data, which is $n_s=0.9649\pm0.0042$ as well as the tensor-to-scalar ratio $r<0.106$ and the e-fold parameter $40<N<70$ for both the potentials.