  A sterile neutrino with mass of several keV can account for cosmological dark
matter, as well as explain the observed velocities of pulsars. We show that
X-rays produced by the decays of these relic sterile neutrinos can boost the
production of molecular hydrogen, which can speed up the cooling of gas and the
early star formation, which can, in turn, lead to a reionization of the
universe at a high enough redshift to be consistent with the WMAP results.
