Z-induced FCNCs and their effects on Neutrino Oscillations
  Adding singlet neutrinos to the standard model spectrum in general gives rise to Z-induced flavor-changing neutral currents. We study the impact of these currents on matter-induced neutrino oscillations in the sun and in supernovae. While the effects for solar neutrinos are negligible, dramatic effects are possible for supernova neutrinos. 
Sven Bergmann, Alex Kagan