Observable induced gravitational waves from an early matter phase
  Assuming that inflation is succeeded by a phase of matter domination, which
corresponds to a low temperature of reheating $T_r<10^9\rm{GeV}$, we evaluate
the spectra of gravitational waves induced in the post-inflationary universe.
We work with models of hilltop-inflation with an enhanced primordial scalar
spectrum on small scales, which can potentially lead to the formation of
primordial black holes. We find that a lower reheat temperature leads to the
production of gravitational waves with energy densities within the ranges of
both space and earth based gravitational wave detectors.
