Energy peak: back to the Galactic Center GeV gamma-ray excess

Understand

We propose a novel mechanism enabling us to have a continuum bump as a signature of gamma-ray excess in indirect detection experiments of dark matter (DM), postulating a generic dark sector having (at least) two DM candidates.

• With the assumption of non-zero mass gap between the two DM candidates, the heavier one directly communicates to the partner of the lighter one.
• Such a partner then decays into a lighter DM particle along with an "axion-like" particle (ALP) or dark "pion", which subsequently decays into a pair of photons, via a more-than-one step cascade decay process.
• Since the cascade is initiated by the dark partner obtaining a non-trivial fixed boost factor, a continuum gamma-ray energy spectrum naturally arises even with a particle directly decaying into two photons.