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

¹ Jockey Club Institute for Advanced Study, The HongKong University of Science andTechnology, HongKong S.A.R., China
² Graduate Schoolof Science, The UniversityofTokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
³ National Astronomical Observatoryof Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁴ School of Physics, International Research Center for Big-Bang Cosmology and Element Genesis, Beihang University, 37, Xueyuan Rd., Haidian-qu, Beijing 100083 China

^* e-mail: iascchao@ust.hk
^** e-mail: yudong.luo@nao.ac.jp
^*** e-mail: kusakabe@buaa.edu.cn
^**** e-mail: kajino@buaa.edu.cn

Published online: 24 February 2022

Abstract

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.