Ultra slow-roll inflation and the non-Gaussianity consistency relation

Abstract

Ultra slow-roll inflation has recently been used to challenge the non-Gaussianity consistency relation. We show that this inflationary scenario belongs to a one-parameter class of models, and we study its properties and observational predictions. We demonstrate that the power spectrum remains scale invariant and that the bispectrum is of the local type with ${f}_{\mathrm{NL}}=5(3\ensuremath{-}{n}_{\mathrm{s}})/4$, which indeed represents a modification of the consistency relation. However, we also show that the system is unstable and suffers from many physical problems among which is the difficulty in correctly WMAP normalizing the model. We conclude that ultra slow-roll inflation remains a very peculiar case, the physical relevance of which is probably not sufficient to call into question the validity of the consistency relation.