Neutrino masses, Large mixings and phenomenology

2001

Ph.D

University of Madras

This thesis concentrates on a few aspects of massive neutrino physics. The effects of matter on neutrino oscillations is described, which are a consequence of massive neutrinos. A short description of the electromagnetic properties of a massive neutrino is presented. Both the matter and electromagnetic effects have been employed in understanding the solar neutrino puzzle. The different aspects of neutrinos, like whether they are Dirac or Majorana in nature, are analyzed. The analysis presented here is general and is valid for an arbitrary number of neutrino flavours. It is found that for the case of Spectrum being quasi-degenerate, the renormalization group extrapolation of a dimension five operator to the low scale can lead to large flavour mixings. This approach requires the Majorana neutrino masses to be in the same CP eigenstate. The mechanism MSSM is quantified, and the relevant constraints due to neutrinoless double beta decay process is found. On the other hand if the masses are hierarchial, it is found that the existence of a sterile neutrino, which is assumed to be the heaviest mass state, can induce large flavour mixings in the active sector as a consequence of its decoupling from the active masses. The popular Zee model for neutrino masses is studied in a more general manner. It is found that all the Majorana masses obtained to be of similar order and the spectrum is inverted just as in the conventional case. In addition the solution to the solar anomaly turns out to be a large mixing angle one, which is currently the most preferred solution. Present analysis of the generalized version of the Zee model does not support the small angle solution.