Electron-, mu-, and tau-number conservation in a supernova core - art. no.093021

We study if the neutrino mixing parameters suggested by the atmospheric neu trino anomaly imply chemical equilibrium between mu- and tau -flavored lept ons in a supernova (SN) core. The initial flavor-conversion rate would inde ed be fast if the nu (mu)-nu (tau)-mixing angle were not suppressed by seco nd-order refractive effects. The neutrino diffusion coefficients are differ ent for nu (mu), <(<nu>)over bar>(mu), nu (tau), and <(<nu>)over bar>(tau) so that neutrino transport will create a net mu and tau lepton number densi ty. This will typically lead to a situation where the usual first-order ref ractive effects dominate, further suppressing the rate of flavor conversion . Altogether, neutrino refraction has the nontrivial consequence of guarant eeing the separate conservation of e, mu, and tau lepton number in a SN cor e on the infall and cooling time scales, even when neutrino mixing angles a re large.