48 pages, 6 figures Typos fixed, text edited for brevity and clarity, references added, minor correction in binary merger rate presented in Appendix B which results in slightly stronger constraints on the EMBH abundance from binary mergers, comments added about bounds evolve if the semi-classical description of Hawking radiation breaks down
We present current direct and astrophysical limits on the cosmological abundance of black holes with extremal magnetic charge. Because they don't Hawking radiate, much lighter primordial black holes could exist today if they are extremal. The dominant constraints come from white dwarf destruction for intermediate masses, and intergalactic gas heating for heavier black holes. Extremal magnetic black holes may catalyze proton decay, and thus we derive robust limits -- independent of the catalysis cross section -- from the above as well as from white dwarf heating. We discuss other bounds such as those from neutron star heating, solar neutrino production, binary formation and annihilation into gamma rays, and magnetic field destruction. We note that stable magnetically charged black holes can assist in the formation of neutron star mass black holes.
Unveiling Primordial Black Hole Relics Through Induced Gravitational Waves
Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study, The University of Tokyo（东京大学宇宙前沿研究机构 物质量子宇宙学柯尔弗里研究所）；Yukawa Institute for Theoretical Physics, Kyoto University（京都大学汤川理论物理研究所）；National Taiwan University（台湾大学）；Asia Pacific Center for Theoretical Physics（亚太理论物理中心）
