  There exists considerable interest in dark matter candidates that can reduce
cosmological structure at sub-galactic scales through a suppression of the
power spectrum of primordial perturbations as well as have a primordial
velocity distribution to produce cores in the smallest-scale dwarf halos. Light
keV-mass-scale sterile neutrinos can be such a "warm" dark matter candidate and
are still viable candidates in broad regions of their parameter space. We
review the status of this candidate and the current constraints from its
radiative decay in the X-ray and from structure formation. We also provide a
forecast for the sensitivity of the International X-ray Observatory to this
decay, which we show may have the ability to detect or exclude sterile
neutrinos within its full parameter space of interest as a dark matter
candidate.
