Gauge singlet scalars as cold dark matter

We consider a very simple extension of the standard model in which one or more gauge singlet scalars S₈ couples to the standard model via an interaction of the form ₒS₈^^S₈H^^H, where H is the standard model Higgs doublet. The thermal relic density of S scalars is calculated as a function of the coupling ₒ and the S scalar mass mₒ. The regions of the (mₒ, ₒ) parameter space which can be probed by present and future experiments designed to detect scattering of S dark matter particles from Ge nuclei, and to observe upward-moving muons and contained events in neutrino detectors due to high-energy neutrinos from annihilations of S dark matter particles in the Sun and the Earth, are discussed. Present experimental bounds place only very weak constraints on the possibility of thermal relic S scalar dark matter. The next generation of cryogenic Ge detectors and of large area (10^4 m^2) neutrino detectors will be able to investigate most of the parameter space corresponding to thermal relic S scalar dark matter up to mₒ50 GeV, while a 1 km^2 detector would in general be able to detect thermal relic S scalar dark matter up to mₒ100 GeV and would be able to detect up to mₒ500 GeV or more if the Higgs boson is lighter than 100 GeV.