Neutrino Mass and Oscillation in Matter and in Cosmology

Abstract

With improved Z-Burst model for the new cosmology and reasonable distribution of the neutrino cosmic ray sources, the signatures of the Z-Burst absorption dip and the contributing parameters are investigated through numerical calculations. From the results of the numerical calculations, it is learned that the source distribution and the neutrino mass spectrum will be the major contributing parameters for the Z-Burst absorption dip. Also, only Z-Burst absorption dip will not be able to offer enough information for to establish the structure of the neutrino mass spectrum.

The heavy neutrino mass of a few $10^{-1}$ eV supported by the four-neutrino model and the LSND mass gap is essential for the detection of the Z-Burst absorption dip. The evidence against the (2+2) neutrino model, especially the Sum Rule, is investigated. Through numerical calculations, it is shown that the small mixing angles, especially $emm$ and $eme$, with the assistance of the MSW matter effect can significantly weaken the Sum Rule. This result casts doubts on the conclusions of the global experiment data fitting, in which two of the small mixing angles $eme$ and $eee$ are set to zero.

With the future extremely high-energy neutrino cosmic ray detectors and the improvement in the neutrino oscillation experiments, the full establishment of the neutrino mass spectrum with the absolute neutrino mass could be achieved in the this decade.