Weakly interacting massive particle densities in decaying-particle-dominated cosmology

We consider the present cosmological density of weakly interacting massive particles (WIMP's) in the context of models where the energy density is dominated by decaying massive particles, such that WIMP's freeze out of chemical equilibrium during the massive-particle-dominated era. An expression for the density of WIMP's is derived by a generalization of the Lee-Weinberg argument for the density of heavy neutrinos in the standard cosmological model.