Resonant spin-flavor conversion of supernova neutrinos and deformation of the electron antineutrino spectrum

The neutrino spin-flavor conversion of <(nu)over bar>(e)<->nu(mu) which is induced by the interaction of the neutrino magnetic moment and magnetic fields in the collapse-driven supernova is investigated in detail. We calculate the conversion probability by using the latest precollapse models of Woosley and Weaver, and also those of Nomoto and Hashimoto, changing the stellar mass and metallicity in order to estimate the effect of the astrophysical uncertainties. Contour maps of the conversion probability are given for all the models as a function of the neutrino mass-squared difference over neutrino energy (Delta m(2)/E(nu)) and the neutrino magnetic moment times magnetic fields (mu(nu)B). The expected deformation of the <(nu)over bar>(e) spectrum can be clearly seen from these maps, and some qualitative features which will be useful in future observations are summarized. It is shown that in the solar metallicity models some observational effects are expected with Delta m(2) = 10(-5)-10(-1) [eV(2)] and mu(nu)greater than or similar to 10(-12)(10(9) G/B-0) [mu(B)], where B-0 is the strength of the magnetic fields at the surface of the iron core, and B-0=10(9) [Gauss] is a reasonable value which is inferred from the observed magnetic fields in white dwarfs. We also find that:although the dependence on the stellar models or stellar mass is not so large, the metallicity of precollapse stars has a considerable effect on this conversion. In lower metallicity stars, strong precession between <(nu)over bar>(e) and nu(mu) occurs with small Delta m(2)/E(nu) (less than or similar to 10(-8) [eV(2)/MeV]), and the conversion probability changes periodically with B-0. Such effects may be seen in a supernova in the Large or Small Magellanic Clouds, and should be taken into account when one considers an upper bound on mu(nu) from the SN 1987A data.