Ultra slow-roll inflation demystified
  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.
