Primordial non-Gaussianity from ultra slow-roll Galileon inflation

TL;DR

This paper investigates how sharp transitions in ultra slow-roll Galileon inflation can produce significant primordial non-Gaussianities, with implications for primordial black hole formation and compliance with theoretical constraints.

Contribution

It demonstrates that sharp SR to USR transitions in Galileon inflation generate large non-Gaussianities and black holes, violating Maldacena's theorem in USR and SRII phases.

Findings

Large non-Gaussianity amplitudes achieved during USR phase

Violations of Maldacena's no-go theorem in USR and SRII phases

Potential for primordial black hole production linked to transition scales

Abstract

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. The non-renormalization theorem in the Galileon theory helps to support our results regarding the generation of large mass primordial black holes along with large non-Gaussianities, which we show to be dependent on the specific positions of the transition wave numbers fixed at low scales.