Primordial non-Gaussianity from ultra slow-roll Galileon inflation

Understand

We present a detailed study of the generation of large primordial non-Gaussianities during the slow-roll (SR) to ultra-slow roll (USR) transitions in the framework of Galileon inflation.

• We found out that due to having sharp transitions in the USR phase, which persist with a duration of $\Delta {\it N}_{\rm USR} \sim 2$ e-folds, we are able to generate the non-Gaussianity amplitude of the order: $|f_{\rm NL}| \sim {\it O}(10^{-2})$ in the SRI, $-5 < f_{\rm NL} < 5$ in the USR, and $-2 < f_{\rm NL} < 2$ in the SRII phases.
• As a result, we are able to achieve a cumulative average value of $|f_{\rm NL}| \sim {\it O}(1)$.
• This implies that our results strictly satisfy Maldacena's no-go theorem in the squeezed limit only for SRI, while they strictly violate the same condition in both the USR and SRII phases.