Electron Neutrino Pair Annihilation: A New Source for Muon and Tau   Neutrinos in Supernovae
  We show that in a supernova core the annihilation process nu_e nu_e-bar -> nu_{mu,tau} nu_{mu,tau}-bar is always more important than the traditional reaction e^+ e^- -> nu_{mu,tau} nu_{mu,tau}-bar 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 hydrodynamical simulation with Boltzmann neutrino transport. Nucleon bremsstrahlung NN -> NN nu_{mu,tau} nu_{mu,tau}-bar is also included as another important source term. Taking into account nu_e nu_e-bar -> nu_{mu,tau} nu_{mu,tau}-bar increases the nu_mu and nu_tau luminosities by as much as 20% while the spectra remain almost unaffected. In our hydrodynamical simulation the shock was somewhat weakened. Elastic nu_{mu,tau} nu_e and nu_{mu,tau} nu_e scattering is not negligible but less important than nu_{mu,tau} e^+ or e^- scattering. Its influence on the nu_{mu,tau} fluxes and spectra is small after all other processes have been included. 
Robert Buras (1 and 2), Hans-Thomas Janka (1), Mathias Th. Keil (2),   Georg G. Raffelt (2), Markus Rampp (1) ((1) Max-Planc...