SIMP dark matter with gauged Z
                            3 symmetry

Soo-Min Choi,Hyun Min Lee

doi:10.1007/jhep09(2015)063

Abstract

We consider a complex scalar field as SIMP dark matter in models with gauged Z 3 discrete symmetry appearing as a remnant of dark local U(1). Dark matter (DM) annihilates dominantly by the 3-to-2 scattering, due to the DM cubic coupling in combination with the DM quartic coupling or the Z′ gauge and dark Higgs couplings. We show that a light Z′ gauge boson makes DM in kinetic equilibrium with thermal plasma at freeze-out and it affects the DM relic density and perturbativity/unitarity constraints for DM self-interactions. We show that the large DM self-interactions are consistent with solving small-scale structure problems and explaining the DM halo separation recently observed in Abell 3827 cluster. Various bounds on the model from the SIMP conditions, DM self-interactions, Z′ searches, DM direct/indirect detection experiments, and Higgs signals, are also discussed.

Highlights

The interactions of a light mediator between SIMP and the SM particles can be probed by various indirect and direct experiments [6]
We show that a light Z′ gauge boson makes Dark matter (DM) in kinetic equilibrium with thermal plasma at freezeout and it affects the DM relic density and perturbativity/unitarity constraints for DM self-interactions
The direct detection of SIMP dark matter with electron recoil [19,20,21] and the bound from indirect detection and the bound from Higgs signals are briefly discussed

Summary

The model

The remaining discrete Z3 symmetry is of the gauge symmetry origin [22, 23] and ensures the stability of scalar dark matter χ. The dark photon communicates between dark matter and the SM particles through the gauge kinetic mixing. As will be shown in a later discussion on SIMP dark matter, the dark photon couplings to the SM fermions become important for keeping dark matter in kinetic equilibrium with the SM. U(1)V symmetry is broken to a discrete subgroup Z3 and dark photon gets massive and can mix with the SM Z-boson. After expanding the dark Higgs as φ = √1 (v′ + h′), the dark Higgs can mix with the SM Higgs by Higgs-portal interaction, λφH. The interaction terms for dark/SM Higgses and dark photon are given in the appendix A

Dynamics of SIMP dark matter

Bounds on SIMP dark matter

Self-scattering cross section

Direct detection

Higgs portal couplings and Higgs signals

Indirect detection

Conclusions

B General formulas for cross sections