Light primordial black holes (LPBHs) with masses in the range $10\mathrm{g}\le M_{\mathrm{BH}}\le {10}^9\mathrm{g}$, although they evaporate before Big Bang Nucleosynthesis, can play a significant role in the production of both dark matter and dark radiation. In particular, LPBHs can evaporate into light axions or axionlike particles (ALPs) with masses $m_a\lesssim \mathrm{MeV}$, contributing to the effective number of neutrino species, $\mathrm{\Delta }{N}_{\mathrm{eff}}$. Additionally, heavy scalar particles known as moduli, predicted by string theory, can be produced both via Hawking evaporation and through amplification by a mechanism called superradiant instability in the case of spinning primoridal black holes (PBHs). These moduli can subsequently decay into ALPs, further amplifying their abundance. In this work, we calculate the number density of ALPs in the presence of moduli enhanced by superradiance for Kerr PBHs. Using current limits on $\mathrm{\Delta }{N}_{\mathrm{eff}}$ from Planck satellite observations, we derive updated constraints on this scenario.

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• Axions
• Cosmology
• Particle astrophysics
• Quantum aspects of black holes