Self-interacting scalar dark matter with local Z3 symmetry

Abstract

We construct a self-interacting scalar dark matter (DM) model with local discrete Z3 symmetry that stabilizes a weak scale scalar dark matter X. The model assumes a hidden sector with a local U(1)X dark gauge symmetry, which is broken spontaneously into Z3 subgroup by nonzero VEV of dark Higgs field ϕX (⟨ϕX⟩≠0). Compared with global Z3 DM models, the local Z3 model has two new extra fields: a dark gauge field Z′ and a dark Higgs field ϕ (a remnant of the U(1)X breaking). After imposing various constraints including the upper bounds on the spin-independent direct detection cross section and thermal relic density, we find that the scalar DM with mass less than 125 GeV is allowed in the local Z3 model, in contrary to the global Z3 model. This is due to new channels in the DM pair annihilations open into Z′ and ϕ in the local Z3 model. Most parts of the newly open DM mass region can be probed by XENON1T and other similar future experiments. Also if ϕ is light enough (a few MeV ≲mϕ≲ O(100) MeV), it can generate a right size of DM self-interaction and explain the astrophysical small scale structure anomalies. This would lead to exotic decays of Higgs boson into a pair of dark Higgs bosons, which could be tested at LHC and ILC.