Electromagnetic Properties  Astrophysical Limits  Neutrino Masses

Neutrino Oscillations

The $\nu_e$, $\bar\nu_e$, and $\nu_{\mu,\tau}$, $\bar\nu_{\mu,\tau}$ supernova fluxes are believed to have different spectra. Therefore, if neutrino oscillations would partially ``swap'' the flavours, the interpretation of the SN 1987A signal would have to be modified, especially if one of the large-angle solutions to the solar neutrino problem (Sec. ) were found to obtain. Resonant oscillations may occur in a SN between $\nu_e$ and $\nu_\mu$ or $\nu_\tau$. For mass differences between a few eV to about $100\,\rm eV$, the matter-induced conversion would occur so close to the neutrino sphere that SN physics itself would be modified. The increased $\nu_e$ energies would help to transfer energy to the stalling shock wave and thus help to explode SNe in the delayed-explosion scenario. Conversely, the spectral swap would cause the $\nu_e$ spectrum to be stiffer than the $\bar\nu_e$ one, so that the neutrino-driven wind from the new-born neutron star is shifted into a proton-rich phase, preventing the r-process nucleosynthesis which is thought to occur in this environment. There is a range of mixing angles in the rough range $10^{-7}\leq\sin^22\theta\leq 10^{-5}$ where the MSW effect could help to explode SNe, and yet not disturb r-process nucleosynthesis.