UC Irvine

We point out that the relic densities of singlet (sterile) neutrinos of interest in viable warm and cold dark matter scenarios depend on the characteristics of the QCD transition in the early universe. In the most promising of these dark matter scenarios, the production of the singlets occurs at or near the QCD transition. Since production of the singlets, their dilution, and the disappearance of weak scatterers occur simultaneously, we calculate these processes contemporaneously to obtain accurate predictions of relic sterile neutrino mass density. Therefore, a determination of the mass and superweak mixing of the singlet neutrino through, for example, its radiative decay, along with a determination of its contribution to the critical density, can provide insight into the finite-temperature QCD transition. © 2002 The American Physical Society.