Redshift Effects in Particle Production from Kerr Primordial Black Holes

Understand

When rotating primordial black holes evaporate via Hawking radiation, their rotational energy and mass are dissipated with different dynamics.

• We investigate the effect of these dynamics on the production of dark radiation -- in the form of hot gravitons or vector bosons -- and non-cold dark matter.
• Although the production of higher-spin particles is enhanced while primordial black holes are rotating, we show that the energy density of dark radiation experiences an extra redshift because their emission effectively halts before PBH evaporation completes.
• We find that taking this effect into account leads to suppression by a factor of $\mathcal{O}(10)$ of $\Delta N_{\rm eff}$ for maximally rotating black holes as compared to previous results.