Anatomy of singlet-doublet dark matter relic: annihilation, co-annihilation, co-scattering, and freeze-in

TL;DR

This paper systematically studies the singlet-doublet dark matter model, including annihilation, co-annihilation, co-scattering, and freeze-in processes, revealing new parameter space regions relevant for collider detection.

Contribution

It introduces the first comprehensive analysis of co-scattering and non-thermal production mechanisms in this dark matter model, expanding understanding of relic density calculations.

Findings

Co-scattering significantly affects relic density calculations.

Correct relic density regions are now within LHC and MATHUSLA detection ranges.

The assumption of simultaneous decoupling for singlet and doublet components is invalid for small mixing angles.

Abstract

The singlet-doublet vector-like fermion dark matter model has been extensively studied in the literature over the past decade. An important parameter in this model is the singlet-doublet mixing angle ($\sin\theta$). All the previous studies have primarily focused on annihilation and co-annihilation processes for obtaining the correct dark matter relic density, assuming that the singlet and doublet components decouple at the same epoch. In this work, we demonstrate that this assumption holds only for larger mixing angles with a dependency on the mass of the dark matter. However, it badly fails for the mixing angle $\sin\theta<0.05$. We present a systematic study of the parameter space of the singlet-doublet dark matter relic, incorporating annihilation, co-annihilation, and, for the first time, co-scattering processes. Additionally, non-thermal productions via the freeze-in and SuperWIMP mechanism are also explored. We found that due to the inclusion of co-scattering processes, the correct relic density parameter space is shifted towards the detection sensitivity range of the LHC and MATHUSLA via displaced vertex signatures.