Nonthermal axino as cool dark matter in the supersymmetric standard model withoutRparity

We point out that the axino predicted as the supersymmetric partner of the axion is a good candidate for the recently proposed sterile neutrino cool dark matter. The axino mass falls into the right range (keV) in the context of gauge-mediated supersymmetry breaking. A sizable mixing of the axino with active neutrinos arises when R-parity violation is allowed and the resulting neutrino masses and mixing accommodate the atmospheric and solar neutrino oscillations simultaneously.