A closer look at dark photon explanations of the excess radio background

Understand

The observed excess radio background has remained a puzzle for over a decade.

• A recent new physics solution involves dark matter that decays into dark photons in the presence of a thermal dark photon background.
• The produced non-thermal dark photon spectrum then converts into standard photons around the reionization era, yielding an approximate power-law radio excess with brightness temperature $T(\nu)\simeq \nu^{-2.5}$ over a wide range of frequencies, $\nu$.
• This simple power-law model comes intriguingly close to the current data, even if several ingredients are required to make it work.