Electron Neutrino Pair Annihilation: A New Source for Muon and Tau Neutrinos in Supernovae

We show that in a supernova core the annihilation process ν_eν_e-->ν_μ,τν_μ,τ is always more important than the traditional reaction e⁺e^--->ν_μ,τν_μ,τ as a source for muon and tau neutrino pairs. We study the impact of the new process by means of a Monte Carlo transport code with a static stellar background model and by means of a self-consistent hydrodynamic simulation with Boltzmann neutrino transport. Nucleon bremsstrahlung NN-->NNν_μ,τν_μ,τ is also included as another important source term. Taking into account ν_eν_e-->ν_μ,τν_μ,τ increases the ν_μ and ν_τ luminosities by as much as 20%, while the spectra remain almost unaffected. In our hydrodynamic simulation, the shock was somewhat weakened. Elastic ν_μ,τν_e and ν_μ,τν_e scattering is not negligible but less important than ν_μ,τe^+/- scattering. Its influence on the ν_μ,τ fluxes and spectra is small after all other processes have been included.