• Corpus ID: 239885476

Evaporating primordial black holes, the string axiverse, and hot dark radiation

@inproceedings{Calz2021EvaporatingPB,
  title={Evaporating primordial black holes, the string axiverse, and hot dark radiation},
  author={Marco Calz{\'a} and John March-Russell and Jo{\~a}o G. Rosa},
  year={2021}
}

• M. Calzá, J. March-Russell, J. G. Rosa
• Published 26 October 2021
• Physics

We show that primordial black holes (PBHs) develop non-negligible spins through Hawking emission of the large number of axion-like particles generically present in string theory compactifications. This is because scalars can be emitted in the monopole mode (l = 0), where no angular momentum is removed from the BH, so a sufficiently large number of scalars can compensate for the spin-down produced by fermion, gauge boson, and graviton emission. The resulting characteristic spin distributions for 10-10 kg PBHs could potentially be measured by future gamma-ray observatories, provided that the PBH abundance is not too small. This yields a unique probe of the total number of light scalars in the fundamental theory, independent of how weakly they interact with known matter. The present local energy density of hot, MeV-TeV, axions produced by this Hawking emission can possibly exceed ρCMB. Evaporation constraints on PBHs are also somewhat weakened.