Impact of dark matter self-scattering on its relic abundance

TL;DR

This paper investigates how dark matter self-scattering influences its relic abundance by altering momentum distributions, revealing scenarios where it significantly affects annihilation efficiency and final dark matter density.

Contribution

It demonstrates that dark matter self-scattering can impact relic abundance calculations by modifying momentum distributions, especially in models with resonant annihilations or additional particle sources.

Findings

Self-scattering can decrease relic abundance under certain conditions.

Momentum distribution modifications are crucial for accurate relic density predictions.

Injection of energetic particles can lead to lower relic abundance.

Abstract

Elastic self-scatterings do not change the number of dark matter particles and as such have been neglected in the calculation of its relic abundance. In this work we highlight the scenarios where the presence of self-scatterings has a significant impact on the effectiveness of annihilation processes through the modification of dark matter momentum distribution. We study a few example freeze-out scenarios involving resonant and sub-threshold annihilations, as well as a model with an additional source of dark matter particles from the decays of a heavier mediator state. Interestingly, when the calculation is performed at the level of dark matter momentum distribution function, we find that the injection of additional energetic dark matter particles onto the thermal population can lead to a $\textit{decrease}$ of its final relic abundance.