Folded Resonant Non-Gaussianity in General Single Field Inflation
Xingang Chen
TL;DR
This work addresses how small periodic features in general single-field inflation can generate large non-Gaussianities. It develops a unified framework for resonant and folded resonant non-Gaussianity by analyzing the cubic action of curvature perturbations and incorporating a small non-Bunch-Davies vacuum component produced by features, with oscillatory couplings of frequency $\omega$ and a background Hubble rate $H$. The authors derive leading-order bispectra: a resonant component $S_{\rm res}$ with oscillations in $\ln K$ and amplitudes scaling as powers of $\omega/H$, and a folded resonant component $S = S_{\lambda} + S_{c}$ that peaks near folded configurations due to the excited negative-energy mode; these results depend on $c_s$, $\lambda/\Sigma$, and the oscillation amplitude $\delta_A$. The findings yield distinctive observational signatures in the CMB and large-scale structure and show that combining resonance, non-Bunch-Davies vacua, and higher-derivative kinetic terms can enhance $f_{NL}$ beyond individual mechanisms.
Abstract
We compute a novel type of large non-Gaussianity due to small periodic features in general single field inflationary models. We show that the non-Bunch-Davies vacuum component generated by features, although has a very small amplitude, can have significant impact on the non-Gaussianity. Three mechanisms are turned on simultaneously in such models, namely the resonant effect, non-Bunch-Davies vacuum and higher derivative kinetic terms, resulting in a bispectrum with distinctive shapes and running. The size can be equal to or larger than that previously found in each single mechanism. Our full results, including the resonant and folded resonant non-Gaussianities, give the leading order bispectra due to general periodic features in general single field inflation.