Light Element Abundances Constrain Primordial Black Holes in the Critical Collapse Model

We study the photodisintegration process triggered by the nonthermal electromagnetic Hawking radiation from primordial black holes (PBHs) in the critical collapse model. The presence of a low-mass tail of critical collapse mass function could enhance energetic photon emissions from Hawking radiation of PBHs. Nuclear photodisintegration rates are calculated with a non-thermal photon spectrum derivedby solving the Boltzmann equation iteratively. Withthenewest observational limitonthe³Heabundancein GalacticHII regions, the updated ³He constraints on PBH mass spectrum in the horizon mass range 10¹²–10¹³gare derived. Our results showthat³He constraints on the critical mass function are about one order of magnitude severer than the monochromatic one, although the fraction of PBHs in the low-mass tail region is relatively small.