Coscattering in next-to-minimal dark matter and split supersymmetry

TL;DR

This paper develops a numerical method to accurately compute dark matter relic density in models where inelastic scattering, or coscattering, dominates, and applies it to a simple electroweak-scale model and split supersymmetry.

Contribution

It introduces a precise numerical approach to solve momentum-dependent Boltzmann equations for coscattering, improving relic density calculations in relevant dark matter models.

Findings

Coscattering can set the relic abundance at small mixing angles.

The method accurately predicts relic density including early kinetic decoupling effects.

Parameter ranges for observed relic abundance are identified in the studied models.

Abstract

In some models of thermal relic dark matter, the relic abundance may be set by inelastic scattering processes (rather than annihilations) becoming inefficient as the universe cools down. This effect has been called coscattering. We present a procedure to numerically solve the full momentum-dependent Boltzmann equations in coscattering, which allows for a precise calculation of the dark matter relic density including the effects of early kinetic decoupling. We apply our method to a simple model, containing a fermionic SU(2) triplet and a fermionic singlet with electroweak-scale masses, at small triplet-singlet mixing. The relic density can be set by either coannihilation or, at values of the mixing angle $\theta\lesssim 10^{-5}$, by coscattering. We identify the parameter ranges which give rise to the observed relic abundance. As a special case, we study bino-like dark matter in split supersymmetry at large $\mu$.