COSMIC MICROWAVE BACKGROUND CONSTRAINTS OF DECAYING DARK MATTER PARTICLE PROPERTIES

If a component of cosmological dark matter is made up of massive particles-such as sterile neutrinos-that decay with cosmological lifetime to emit photons, the reionization history of the universe would be affected, and cosmic microwave background anisotropies can be used to constrain such a decaying particle model of dark matter. The optical depth depends rather sensitively on the decaying dark matter particle mass m(dm), lifetime tau(dm), and the mass fraction of cold dark matter f that they account for in this model. Assuming that there are no other sources of reionization and using the Wilkinson Microwave Anisotropy Probe 7-year data, we find that 250 eV less than or similar to m(dm) less than or similar to 1 MeV, whereas 2.23 x 10(3) yr less than or similar to tau(dm)/f less than or similar to 1.23 x 10(18) yr. The best-fit values for m(dm) and tau(dm)/f are 17.3 keV and 2.03 x 10(16) yr, respectively.