Observational Constraints on the $f(\phi,T)$ gravity theory

Abstract

We investigate inflation in modified gravity framework by introducing a direct coupling term between a scalar field $\phi$ and the trace of the energy momentum tensor $T$ as $f(\phi,T) = 2 \phi( \kappa^{1/2} \alpha T + \kappa^{5/2} \beta T^2) $ to the Einstein-Hilbert action. We consider a class of inflaton potentials (i) $V_0 \phi^p e^{-\lambda\phi}$, (ii) $V_0\frac{ \lambda \phi^p}{1+\lambda\phi^p}$ and investigate the sensitivity of the modified gravity parameters $\alpha$ and $\beta$ on the inflaton dynamics. We derive the potential slow-roll parameters, scalar spectral index $n_s$, and tensor-to-scalar ratio $r$ in the above $f(\phi,T)$ gravity theory and analyze the following three choices of modified gravity parameters~(i) Case I:~ $\alpha \neq 0, ~\beta=0$ i.e. neglecting higher order terms, (ii) Case II:~ $\alpha=0$, $\beta \neq 0$~ and do the analysis for $T^2$ term, (iii) Case III:~ $\alpha \neq 0$ and $\beta \neq 0$ i.e. keeping all terms. For a range of potential parameters, we obtain constraints on $\alpha$ and $\beta$ in each of the above three cases using the WMAP and the PLANCK data.