Dark matter from primordial black holes would hold charge

TL;DR

This paper investigates the potential for primordial black holes to carry electric charge today, considering formation conditions, discharge processes, and interactions with dark matter plasma, which could impact their role as dark matter candidates.

Contribution

It introduces the idea that primordial black holes can retain charge due to formation fluctuations and magnetic shielding, providing new insights into their properties as dark matter.

Findings

Primordial black holes can hold a non-zero charge at formation.

Maximally rotating PBHs may produce magnetic fields that prevent discharge.

Charge-to-mass ratios are within specific ranges for dark matter PBHs.

Abstract

We explore the possibility that primordial black holes (PBHs) contain electric charge down to the present day. We find that PBHs should hold a non-zero net charge at their formation, due to either Poisson fluctuations at horizon crossing or high-energy particle collisions. Although initial charge configurations are subject to fast discharge processes through particle accretion or quantum particle emission, we show that maximally rotating PBHs could produce magnetic fields able to shield them from discharge. Moreover, given that electrons are the lightest and fastest charge carriers, we show that the plasma within virialised dark matter haloes can endow PBHs with net negative charge. We report charge-to-mass ratios between $10^{-31}\,C/\mbox{kg}$ and $10^{-15}\,C/\mbox{kg}$ for PBHs within the mass windows that allow them to constitute the entirety of the dark matter in the Universe.