Primordial black holes from modified supergravity
  The modified supergravity approach is applied to describe a formation of
Primordial Black Holes (PBHs) after Starobinsky inflation. Our approach
naturally leads to the two-(scalar)-field attractor-type double inflation,
whose first stage is driven by scalaron and whose second stage is driven by
another scalar field which belongs to a supergravity multiplet. The scalar
potential and the kinetic terms are derived, the vacua are studied, and the
inflationary dynamics of those two scalars is investigated. We numerically
compute the power spectra and we find the ultra-slow-roll regime leading to an
enhancement (peak) in the scalar power spectrum. This leads to an efficient
formation of PBHs. We estimate the masses of PBHs and we find their density
fraction (as part of Dark Matter). We show that our modified supergravity
models are in agreement with inflationary observables, while they predict the
PBH masses in a range between $10^{16}$ g and $10^{20}$ g. In this sense,
modified supergravity provides a natural top-down approach for explaining and
unifying the origin of inflation and the PBHs Dark Matter.
