Primordial black holes and secondary gravitational waves from string
  inspired general no-scale supergravity
  The formation of primordial black hole (PBH) dark matter and the generation
of scalar induced secondary gravitational waves (SIGWs) have been studied in
the generic no-scale supergravity inflationary models. By adding an exponential
term to the K\"ahler potential, the inflaton experiences a period of
ultraslow-roll and the amplitude of primordial power spectrum at small scales
is enhanced to $\mathcal{O}(10^{-2})$. The enhanced power spectra of primordial
curvature perturbations can have both sharp and broad peaks. A wide mass range
of PBHs can be produced in our model, and the frequencies of the accompanied
SIGWs are ranged form nanohertz to kilohertz. We show four benchmark points
where the generated PBH masses are around $\mathcal{O}(10^{-16}M_{\odot})$,
$\mathcal{O}(10^{-12}M_{\odot})$, $\mathcal{O}(10^{-2}M_{\odot})$ and
$\mathcal{O}(10^{2}M_{\odot})$. The PBHs with masses around
$\mathcal{O}(10^{-16}M_{\odot})$ and $ \mathcal{O}(10^{-12}M_{\odot})$ can make
up almost all the dark matter, and the accompanied SIGWs can be probed by the
upcoming space-based gravitational wave observatory. Also, the SIGWs
accompanied with the formation of stellar mass PBHs can be used to interpret
the stochastic GW background in the nanohertz band, detected by the North
American Nanohertz Observatory for gravitational waves, and can be tested by
future interferometric gravitational wave observatory.
