Generational Mass Splitting of Neutrinos in High Temperature   $SU(2)_{\scriptscriptstyle{L}}\otimes U(1)$ Gauge Theory
  We calculate the generational mass splitting of neutrinos in high temperature $SU(2)_{\scriptscriptstyle{L}}\otimes U(1)$ gauge theory when the temperature is above $250$ GeV and the gauge symmetry is restored. We consider the case of neutrinos that are massless at tree level as well as the case of neutrinos with tree-level mass and large mixing. 
A. Erdas, C. W. Kim and J. A. Lee