Vector dark matter annihilation with internal bremsstrahlung

TL;DR

This paper explores how internal bremsstrahlung can lift chirality suppression in spin-1 dark matter annihilation, especially when dark matter is polarized, affecting the photon spectrum and normalization.

Contribution

It introduces a scenario where polarization enables internal bremsstrahlung to lift suppression in spin-1 dark matter annihilation, with implications for spectral shape and normalization.

Findings

Photon spectrum shape matches that of spin-0 and spin-1/2 dark matter.

Normalization is less suppressed with heavy mediators.

Polarization is crucial for lifting chirality suppression.

Abstract

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.