Relic neutrino asymmetry generation from $\nu_{\alpha}- \nu_s$   oscillations
  Active--sterile neutrino oscillations provide a mechanism by which large differences in the neutrino and antineutrino number densities can be created in the early universe. The quantum kinetic equations are employed in the study of these asymmetries, which, when solved analytically in the adiabatic limit, generate physically transparent evolution equations that are very useful for the understanding of the nature of the asymmetry growth. 
Yvonne Y. Y. Wong