Primordial black holes from an inflationary potential valley

Primordial black holes (PBHs) could be formed if large perturbations are generated on small scales in inflation. We study a toy inflation model with a local minimum. The curvature perturbations are enhanced when the inflaton passes through the local minimum, with more efficient amplification rate than that of quasi-inflection point inflation, leading to the production of PBHs on small scales. The PBHs could comprise the total dark matter in the mass window ${10}^{16}$–${10}^{20}$g.