  We propose that a hierarchical spectrum of sterile neutrinos (eV, keV,
$10^{13-15}$ GeV) is considered to as the explanations for MiniBooNE and LSND
oscillation anomalies, dark matter, and baryon asymmetry of the universe (BAU)
respectively. The scenario can also realize the smallness of active neutrino
masses by seesaw mechanism.
