Enhancement of the sterile neutrinos yield at high matter density and at   increasing the medium neutronization
  The relative yields of active and sterile neutrinos in the matter with a high density and different degree of neutronization are calculated. A significant increase in the proportion of sterile neutrinos produced in superdense matter when degree of neutronization approaches the value of two is found. The results obtained can be used in the calculations of the neutrino fluxes for media with a high density and different neutronization degrees in astrophysical processes such as the formation of protoneutron core of a supernova. 
V. V. Khruschov, A. V. Yudin, D. K. Nadyozhin, and S. V. Fomichev
hep-ph astro-ph.SR