Vector dark matter annihilation with internal bremsstrahlung

Understand

We consider scenarios in which the annihilation of self-conjugate spin-1 dark matter to a Standard Model fermion-antifermion final state is chirality suppressed, but where this suppression can be lifted by the emission of an additional photon via internal bremsstrahlung.

• We find that this scenario can only arise if the initial dark matter state is polarized, which can occur in the context of self-interacting dark matter.
• In particular, this is possible if the dark matter pair forms a bound state that decays to its ground state before the constituents annihilate.
• We show that the shape of the resulting photon spectrum is the same as for self-conjugate spin-0 and spin-1/2 dark matter, but the normalization is less heavily suppressed in the limit of heavy mediators.