Uphill inflation

Primordial black holes (PBH) may form from large cosmological perturbations, produced during inflation when the inflaton's velocity is sufficiently slowed down. This usually requires very flat regions in inflationary potential. In this paper we investigate another possibility, namely that inflaton climbs up its When it turns back, crosses zero, which triggers a short phase of ``uphill inflation'' perturbations grow at fast rate. naturally occurs double-well potentials if width well close to Planck scale. We include effect quantum diffusion scenario, plays crucial role, by means stochastic-$\delta N$ formalism. find ultra-light are with high abundances, do not depend on energy scale uphill occurs, and suffer substantially less fine tuning than alternative PBH-production models. They such PBHs later drive PBH domination.