Primordial Black Holes Evaporating before Big Bang Nucleosynthesis
arXiv:2509.05618 · doi:10.1088/1475-7516/2026/02/063
Abstract
Primordial black holes (PBHs) formed from the collapse of density fluctuations provide a unique window into the physics of the early Universe. Their evaporation through Hawking radiation around the epoch of Big Bang nucleosynthesis (BBN) can leave measurable imprints on the primordial light-element abundances. In this work, we analyze in detail the effects of PBHs evaporating before BBN, with various intermediate steps understood analytically, and obtain the BBN constraint on PBHs within a transparent and reproducible framework. We find that, to produce observable effects on BBN, the PBH mass must exceed g, a threshold higher than that reported in some earlier studies. Slightly above g, the BBN sensitivity rapidly increases with the mass and then decreases, with the turning point occurring at g. For PBHs in the mass range g, current measurements of BBN observables set an upper bound on the initial mass fraction parameter ranging from to . To facilitate future improvements, we make our code publicly available, enabling straightforward incorporation of updated nuclear reaction rates, particle-physics inputs, and cosmological data.
26 pages, 7 figures, a few typos in equations fixed, code available at https://github.com/Fenyutanchan/Primordial-Black-Hole.git
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