Inflationary universe in a conformally-invariant two scalar-field theory with an $R^2$ term

TL;DR

This paper explores a conformally-invariant two-scalar-field inflationary model with an $R^2$ term, demonstrating compatibility with Planck data and the possibility of graceful exit from inflation.

Contribution

It introduces a novel inflationary model with two scalar fields and an $R^2$ term, analyzing slow-roll dynamics and observational viability.

Findings

Spectral index compatible with Planck data

Tensor-to-scalar ratio within observational bounds

Graceful exit from inflation achieved

Abstract

We investigate the inflationary universe in a theory where two scalar fields non-minimally coupling to the scalar curvature and an extra $R^2$ term exist and the conformal invariance is broken. In particular, the slow-roll inflation is explored for the case that one scalar field is dynamical and that two scalar fields are dynamical. As a result, we show that the spectral index of the curvature perturbations and the tensor-to-scalar ratio of the density perturbations can be compatible with the Planck results. It is also demonstrated that the graceful exit from inflation can be realized.