Thermally Generated Gauge Singlet Scalars as Self-Interacting Dark Matter

We show that a gauge singlet scalar S, with a coupling to the Higgs doublet of the form ₒS^SH^H and with the S mass entirely generated by the Higgs expectation value, has a thermally generated relic density ₒ0. 3 if mₒ (2. 9--10. 5) (ₒ/0. 3) ^1/5 (h/0. 7) ^2/50ex{0ex}MeV. Remarkably, this is very similar to the range mₒ0ex{0ex}=0ex{0ex} (6. 6--15. 4) ^2/30ex{0ex}MeV required in order for the self-interaction (/4) (S^S) ^2 to account for self-interacting dark matter when is not much smaller than 1. The corresponding coupling is ₒ (2. 710^-10--3. 610^-9) (ₒ/0. 3) ^2/5 (h/0. 7) ^4/5, implying that such scalars are very weakly coupled to the standard model sector.