Background of radio photons from primordial black holes

Understand

We compute the isotropic radiation background due to Hawking emission from primordial black holes (PBHs), and examine if this background is a viable option in explaining the excess radiowave background observed by the ARCADE2 and LWA1 experiments at $\lesssim 1\,$GHz.

• We find that even under the extreme assumption that all of the dark matter is in the form of PBHs, the radio brightness temperature induced by Hawking evaporation of PBHs is $\mathcal{O}(10^{-46})\,$K, highly subdominant compared to the cosmic microwave background.
• The main reason for this is that for PBHs in the mass range $\sim10^{12}$-$10^{14}\,$kg, which can be constrained by Hawking emission, the spectrum peaks at $10^7$ to $10^5\,$eV.
• As the Hawking spectrum is power law suppressed towards lower energies, negligible flux of $\mu$eV photons is obtained.