Scalar induced gravitational waves in inflation with gravitationally
  enhanced friction
  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.
