Constraints on the primordial curvature power spectrum from primordial
  black holes
  Large-amplitude density perturbations may have collapsed during the radiation
dominated epoch of the Universe to form primordial black holes (PBHs). There
are several constraints to the abundance of PBHs that stem from evaporation or
gravitational effects. Due to the connection between primordial perturbations
and the formation of PBHs, constraints on the present-day abundance of PBHs can
be translated into limits on the primordial curvature power spectrum. We
introduce several new observational and forecasted constraints to the amplitude
of the primordial power spectrum and incorporate in our analysis uncertainties
in the critical overdensity for collapse and considerations of ellipsoidal
collapse. Our results provide the most stringent limits from PBHs on the
primordial curvature power spectrum on small scales.
