Generational Mass Splitting of Neutrinos in High Temperature $SU(2{)}_L\otimes U(1)$ Gauge Theory

We calculate the generational mass splitting of neutrinos in high temperature $SU(2{)}_L\otimes U(1)$ 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.