Systematics of Constant Roll Inflation

TL;DR

This paper systematically explores constant roll inflation models, including newly discovered stable solutions that can produce observationally consistent, nearly scale-invariant spectra without relying on the slow roll approximation.

Contribution

It introduces a new class of stable constant roll inflation models and analyzes their observational viability, expanding the understanding beyond traditional slow roll scenarios.

Findings

Identified a new class of stable constant roll inflation models.

Found parameter regions producing nearly scale-invariant spectra.

Demonstrated stability of these models under scalar perturbations.

Abstract

We study constant roll inflation systematically. This is a regime, in which the slow roll approximation can be violated. It has long been thought that this approximation is necessary for agreement with observations. However, recently it was understood that there can be inflationary models with a constant, and not necessarily small, rate of roll that are both stable and compatible with the observational constraint $n_s \approx 1$. We investigate systematically the condition for such a constant-roll regime. In the process, we find a whole new class of inflationary models, in addition to the known solutions. We show that the new models are stable under scalar perturbations. Finally, we find a part of their parameter space, in which they produce a nearly scale-invariant scalar power spectrum, as needed for observational viability.