Ultra slow-roll inflation demystified

TL;DR

This paper investigates ultra-slow-roll inflation, a regime where the inflaton traverses a flat potential region, analyzing its duration, conditions for its occurrence, and implications for inflection-point inflation.

Contribution

It provides estimates for the duration of USR based on initial conditions and clarifies when standard slow-roll approximations are applicable.

Findings

USR duration depends on initial kinetic density

Small initial kinetic density can prevent USR

Implications for modeling inflection-point inflation

Abstract

Ultra-slow-roll (USR) inflation is a new mode of inflation which corresponds to the occasions when the inflaton field must traverse an extremely flat part of the scalar potential, when the usual slow-roll (SR) fails. We investigate USR and obtain an estimate for how long it lasts, given the initial kinetic density of the inflaton. We also find that, if the initial kinetic density is small enough, USR can be avoided and the usual SR treatment is valid. This has important implications for inflection-point inflation.