Constraining the primordial black hole abundance through Big-Bang nucleosynthesis

TL;DR

This paper explores how evaporating primordial black holes during Big-Bang nucleosynthesis affect light element abundances, providing new constraints on their initial abundance in a specific mass range.

Contribution

It introduces a numerical framework incorporating PBH evaporation effects into BBN calculations, yielding the strongest constraints to date on PBH abundance for masses between 10^8 g and 10^9 g.

Findings

Derived upper bounds on PBH abundance in the 10^8 g to 10^9 g mass range.

Demonstrated how PBH evaporation modifies the universe's expansion and nucleosynthesis.

Provided numerical solutions integrating non-standard Hubble rate and baryon-to-photon ratio.

Abstract

We investigate the scenario in which primordial black holes (PBHs) with masses Mpbh < 10^9 g undergo Hawking evaporation, around the Big-Bang nucleosynthesis (BBN) epoch. The evaporation process modifies the Universe's expansion rate and the baryon-to-photon ratio, leading to an alteration of the primordial abundance of light nuclei. We present numerical solutions for the set of equations describing this physics, considering different values of PBH masses and abundances at their formation, showing how their evaporation impacts the abundances of light nuclei, obtained by incorporating the non-standard Hubble rate and baryon-to-photon ratio into the BBN code PArthENoPE. The results are then used to place upper bounds for the PBH relative abundance at formation in the range 10^8 g < Mpbh < 10^9 g, providing the strongest constraints existing to-date in this mass range.