Scalar induced gravitational waves in inflation with gravitationally enhanced friction

TL;DR

This paper investigates how gravitationally enhanced friction during inflation amplifies scalar perturbations, leading to detectable gravitational waves and primordial black holes, with specific spectral features that can serve as observational signatures.

Contribution

It introduces the GEF mechanism with nonminimal derivative coupling to produce distinctive scalar-induced gravitational wave spectra during inflation.

Findings

GW spectra can reach future detection sensitivities

The power spectrum near the peak follows a power-law form

The UV slope of GW spectrum is twice that of the curvature perturbations

Abstract

We study the scalar induced gravitational wave (GW) background in inflation with gravitationally enhanced friction (GEF). The GEF mechanism, which is realized by assuming a nonminimal derivative coupling between the inflaton field and gravity, is used to amplify the small-scale curvature perturbations to generate a sizable amount of primordial black holes. We find that the GW energy spectra can reach the detectable scopes of the future GW projects, and the power spectrum of curvature perturbations has a power-law form in the vicinity of the peak. The scaling of the GW spectrum in the ultraviolet regions is two times that of the power spectrum slope, and has a lower bound. In the infrared regions, the slope of the GW spectrum can be described roughly by a log-dependent form. These features of the GW spectrum may be used to check the GEF mechanism if the scalar induced GWs are detected in the future.