Ultra slow-roll inflation demystified

Understand

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.