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) over bar (e) --> nu(mu,tau)(nu) over bar (mu,tau) is always more important than the traditional reaction e(+)e(-) --> nu(mu,tau)(nu) over bar (mu,tau) 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 --> NN nu(mu,tau)(nu) over bar (mu,tau) is also included as another important source term. Taking into account nu(e)(nu) over bar (e) --> nu(mu,tau)(nu) over bar (mu,tau) increases the nu(mu) and nu(tau) luminosities by as much as 20%, while the spectra remain almost unaffected. In our hydrodynamic simulation, the shock was somewhat weakened. Elastic nu(mu,tau)nu(e) and nu(mu,tau)(nu) over bar (e) scattering is not negligible but less important than nu(mu,tau)e(+/-) scattering. Its influence on the nu(mu,tau) fluxes and spectra is small after all other processes have been included.