# Inflation with $f(R,\phi)$ in Jordan frame

## TL;DR

This paper analyzes an $f(R)$ gravity model non-minimally coupled to a massive scalar field in the Jordan frame, deriving exact solutions and comparing predicted spectra with observations to study inflationary dynamics.

## Contribution

It provides an exact analytical solution in the Jordan frame for an $f(R,\, ext{scalar})$ model and evaluates its inflationary predictions without frame ambiguity.

## Key findings

- Model produces accelerated expansion with exit.
- Scalar and tensor spectra are computed and compared with observations.
- The approach avoids frame dependence issues.

## Abstract

We consider an $f(R)$ action that is non-minimally coupled to a massive scalar field. The model closely resembles scalar-tensor theory and by conformal transformation can be transformed to Einstein frame. To avoid the ambiguity of the frame dependence, we obtain an exact analytical solution in Jordan frame and show that the model leads to a period of accelerated expansion with an exit. Further, we compute the scalar and tensor power spectrum for the model and compare them with observations.