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Part IV. Neutrino astrophysics

Abstract

We discuss how the neutrino material-heating rate and electron fraction in the region above the neutrino-sphere in a nascent type II supernova become very sensitive to neutrino flavor mixings. Matter-enhancement effects would ensure that a v or v (hereafter, v ) neutrino with a vacuum mass of roughly 10 to 100 eV would have a mass-level-crossing with a light v in this region. Coincidentaly, this is the neutrino mass range which is sometimes conjectured to provide the closure density for the universe. Since the supernova ν neutrinos have considerably higher average energies than do the ν , transformations between these species at the level crossings result in more energetic electron neutrinos. This would imply an enhanced ν capture rate which, in turn, would result in a higher heating rate and would tend to increase the electron fraction, reducing the neutron excess. For vacuum mixing angle between ν and ν of θ>10 the increase in early heating results in roughly a factor of two increase in supernova explosion energy, which may help solve the explosion-mechanism problem. However, late neutrino flavor conversion will drive the ejected material proton-rich and a promising site for r-process nucleosynthesis may be lost unless it is also true that θ < 10 . © 1993. μ τ τ e τ e e τ e -4 -3

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