Speaker
Description
Near-threshold effects such as Sommerfeld enhancement and bound-state formation can substantially modify the thermal freeze-out of dark matter interacting through long-range forces. Over the past years, considerable theoretical progress has led to increasingly precise descriptions of these effects within non-relativistic effective field theories and their thermal extensions. However, implementing the corresponding interaction rates in practical relic-density calculations often remains technically demanding and computationally expensive.
In this work, we develop a simplified and transparent framework to efficiently incorporate Sommerfeld enhancement and bound-state effects into dark matter freeze-out calculations. Focusing on an Abelian dark matter model with fermionic dark matter coupled to a light vector mediator, we systematically analyze the relevant annihilation, bound-state formation, dissociation, and transition rates within the pNREFT framework. We then construct analytic approximations for the thermally averaged interaction rates, including thermal corrections, that accurately reproduce the exact results across the parameter space relevant for freeze-out.
Using these approximated rates, we study the dark matter relic abundance both through direct numerical solutions of the Boltzmann equation and via semi-analytic methods. We show that the resulting simplified treatment captures the dominant non-perturbative dynamics while maintaining good agreement with the full calculation. In particular, the relic density can be reproduced with percent-level accuracy while substantially reducing the computational complexity associated with bound-state dynamics. Our results provide a practical strategy to include near-threshold effects in phenomenological dark matter studies and offer a complementary approach to existing numerical implementations and public tools.