Primordial non-Gaussianity from ultra slow-roll Galileon inflation

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 $\Delta N_{\mathrm{USR}}\sim 2$ e-folds, we are able to generate the non-Gaussianity amplitude of the order: $|f_{\mathrm{NL}}|\sim O(10^{-2})$ in the SRI, $-5<f_{\mathrm{NL}}<5$ in the USR, and $-2<f_{\mathrm{NL}}<2$ in the SRII phases. As a result, we are able to achieve a cumulative average value of $|f_{\mathrm{NL}}|\sim O(1)$. 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.

Comments: 51 pages, 11 figures, 1 table, Typos corrected, and new references added, Comments are welcome, Revised version accepted for publication in JCAP