Scalar and Fermion Two-component SIMP Dark Matter with an Accidental $\mathbb{Z}^{}_4$ Symmetry

TL;DR

This paper introduces a novel two-component SIMP dark matter model with scalar and fermion candidates stabilized by an accidental $ ext{Z}_4$ symmetry, highlighting the importance of two-loop processes in DM relic density and self-interactions.

Contribution

It constructs the first two-component SIMP DM model with an accidental $ ext{Z}_4$ symmetry and analyzes the impact of two-loop processes on DM phenomenology.

Findings

Two-loop induced 2→2 processes significantly affect DM relic density.

The model predicts modified self-interaction cross sections for DM.

Kinetic equilibrium is maintained via gauge couplings until freeze-out.

Abstract

In this paper, we construct for the first time a two-component strongly interacting massive particles (SIMP) dark matter (DM) model, where a complex scalar and a vector-like fermion play the role of the SIMP DM candidates. These two particles are stable due to an accidental $\mathbb{Z}^{}_4$ symmetry after the breaking of a $\text{U}(1)^{}_\textsf{D}$ gauge symmetry. By introducing one extra complex scalar as a mediator between the SIMP particles, this model can have $3 \to 2$ processes that determine the DM relic density. On the other hand, the SIMP DM particles can maintain kinetic equilibrium with the thermal bath until the DM freeze-out temperature via the $\text{U}(1)^{}_\textsf{D}$ gauge couplings. Most importantly, we find an unavoidable two-loop induced $2 \to 2$ process tightly connecting to the $3 \to 2$ process that would redistribute the SIMP DM number densities after the chemical freeze-out of DM. Moreover, this redistribution would significantly modify the predictions of the self-interacting cross section of DM compared with other SIMP models. It is crucial to include the two-loop induced $2 \to 2$ annihilations to obtain the correct DM phenomenology.