Slow-roll inflation in $f\left(R, T, R_{ab}T^{ab}\right)$ gravity

TL;DR

This paper explores slow-roll inflation within a complex modified gravity framework, deriving equations of motion, analyzing different potentials, and studying scalar field behavior under perturbations, extending inflation models in alternative gravity theories.

Contribution

It introduces the slow-roll inflation analysis in $f(R, T, R_{ab}T^{ab})$ gravity, deriving fundamental equations and examining scalar field dynamics with various potentials.

Findings

Equations reduce to $f(R, T)$ gravity form under slow-roll.

Calculated slow-roll parameters and e-folding numbers for different potentials.

Analyzed scalar field perturbations ignoring metric effects.

Abstract

In the framework of $f\left(R, T, R_{ab}T^{ab}\right)$ gravity theory, the slow-roll approximation of the cosmic inflation is investigated, where $T$ is the trace of the energy-momentum tensor $T^{ab}$, $R$ and $R_{ab}$ are the Ricci scalar and tensor, respectively. After obtaining the equations of motion of the gravitational field from the action principle in the spatially flat FLRW metric, the fundamental equations of this theory are received by introducing the inflation scalar field as the matter and taking into account only the minimum curvature-inflation coupling term. Remarkably, after taking the slow-roll approximation, the identical equations as in $f(R, T)$ gravity with a $RT$ mixing term are derived. Several potentials of interest in different domains are evaluated individually, calculating the slow-roll parameter and the e-folding number $N$. Finally, we analyze the behavior of the inflation scalar field under perturbation while ignoring the effect of metric perturbations. This research complements the slow-roll inflation in the modified theory of gravity.