Thermally Generated Gauge Singlet Scalars as Self-Interacting Dark Matter

Abstract

We show that a gauge singlet scalar S, with a coupling to the Higgs doublet of the form lambda_{S} S^{\dagger}S H^{\dagger}H and with the S mass entirely generated by the Higgs expectation value, has a thermally generated relic density Omega_{S} \approx 0.3 if m_{S} \approx (2.9-10.5)(Omega_{S}/0.3)^{1/5}(h/0.7)^{2/5} MeV for Higgs boson masses in the range 115 GeV to 1 TeV. Remarkably, this is very similar to the range (m_{S} = (6.6-15.4)\eta^{2/3} MeV) required in order for the self-interaction (\eta/4)(S^{\dagger}S)^{2} to account for self-interacting dark matter when \eta is not much smaller than 1. The corresponding coupling is lambda_{S} \approx (2.7 \times 10^{-10} - 3.6 \times 10^{-9})(Omega_{S}/0.3)^{2/5}(h/0.7)^{4/5}, implying that such scalars are very weakly coupled to the Standard Model sector.