Selected topics in solar and astrophysical neutrinos

Abstract

This work discusses solar neutrinos, low energy atmospheric neutrinos and supernova neutrinos. It is shown that the low energy atmospheric neutrino anomaly can be explained by vμ - ve or vμ - vτ vacuum oscillations. Vacuum neutrino oscillations, as well as matter enhanced neutrino oscillations can also solve the solar neutrino problem. The vacuum oscillations solution to the solar neutrino problem further predicts large seasonal variations in the solar 7Be neutrino flux. Neutrino decay is also shown to be a possible solution to the solar neutrino problem. Two explicit decay models are proposed, one in which the neutrinos are Dirac particles, and the other in which the neutrinos are Majorana particles. It is shown that both of these models can incorporate neutrino masses and mixings in the right range to explain the low energy atmospheric neutrino oscillations by vμ - ve oscillations, and furthermore, the Majorana neutrino decay model predicts a detectable solar ̄ve flux. Finally the expected neutrino flux from a galactic supernova is discussed, and it is shown that such an event will result in large neutrino signals in the K-II, SuperkamioKande, SNO and Borexino detectors. We further find that examination of the time structure of these signals allows measurements of the vμ and vτ masses in the range 200 < eV < 45 keV) provided they are stable. Unstable neutrinos can give rise to a time delayed ve signal, provided they decay into ̄ve +J, where J is a Majoron.