Physics of supernova neutrinos: flavor conversion effects

Abstract

I review the effects of flavor conversion of neutrinos from stellar collapse due to masses and mixing, and discuss the motivations for their study. I consider in detail the sensitivity of certain observables (characteristics of the energy spectra of nu_e and antinu_e events) to the 13-mixing (sin^2θ_13) and to the type of mass hierarchy/ordering (sign[Delta m^2_13]). These observables are: the ratio of average energies of the spectra, r_E = /<\bar E >, the ratio of widths of the energy distributions, r_Gamma = Gamma/\bar Gamma, the ratios of total numbers of nu_e and antinu_e events at low energies, S, and in the high energy tails, R_tail. I show that regions in the space of observables r_E, r_Gamma, R_tail exist in which certain mass hierarchy and intervals of sin^2θ_13 can be identified or discriminated. Finally, I discuss the potential of studying regeneration effects on nu_e and antinu_e in the matter of the Earth and point out that both the observation or exclusion of these effects lead to model-independent information on sin^2θ_13 and the mass hierarchy. The extraction of this information would highly benefit from the presence of a new, large, long lived nu_e detector, and from the progress of theoretical predictions of the fluxes and energy spectra of the neutrinos originally produced in the star.