The mu and tau number of supernovae

The neutrino-nucleon cross section is slightly larger than that for ν̄−N. Therefore, ν̄ will escape more quickly from core collapse supernovae leaving the star ν rich. A diffusion formalism is used to calculate the time evolution of the mu and tau lepton number densities. These quickly reach steady state equilibria. We estimate that a protoneutron star with a maximum temperature near 50 MeV will contain over 50% more νμ and ντ than ν̄μ and ν̄τ. Supernovae may be the only known systems with large mu and or tau lepton numbers.