Resonance enhancement of dark matter interactions: the case for early kinetic decoupling and velocity dependent resonance width

Understand

Motivated by the possibility of enhancing dark matter (DM) self-interaction cross-section $\sigma_{\rm self}$, we have revisited the issue of DM annihilation through a Breit-Wigner resonance.

• In this case thermally averaged annihilation cross-section has strong temperature dependence, whereas elastic scattering of DM on the thermal bath particles is suppressed.
• This leads to the early kinetic decoupling of DM and an interesting interplay in the evolution of DM density and temperature that can be described by a set of coupled Boltzmann equations.
• The standard Breit-Wigner parametrization of a resonance propagator is also corrected by including momentum dependence of the resonance width.