Growth of power spectrum due to decrease of sound speed during inflation

We study the amplification of curvature perturbations due to a small sound speed and find that its origin is different completely from ultraslow-roll inflation. This because when very enhancement power spectrum comes fact at scales smaller than cosmic microwave background (CMB) scale becomes scale-variant, rather growing leads during At large remains be invariant, which consistent with CMB observations, then it will have transient $k^2$ growth finally approach $k^4$ as smaller. Thus can enhanced generate sizable amount primordial black holes. Furthermore, high order correction in dispersion relation considered has same case without this correction.