| Summary: | 碩士 === 國立清華大學 === 物理系 === 103 === The phenomenon of neutrino oscillation has been established. It implies
that neutrinos having masses, so the mass eigenstate is different with the
flavor eigenstate. They has mixing matrix described by a 3 × 3 unitary matrix,
PMNS, like CKM matrix in quark sector. The most famous pattern is
Tri-Bimaximal mixing matrix which predicts a vanishing θ13, but we have
experimental evidence for a non vanishing value of the smallest θ13. TriBimaximal
mixing matrix needs modifications. We study discrete flavour
symmetries model(A4 symmetry), higher symmetry model and sterile neutrinos
to explain small angle. First, suppose there has A4 symmetry or higher
symmetry in lepton sector and neutrino sector and neutrinos have Majorana
masses(or only have Dirac neutrinos). We will get Tri-Bimaximal mixing
in A4 model. Second, Adding sterile neutrinos modify the mixing matrix,
therefore we could get small angle(θ13). Then, transforming with new mixing
matrix, we found ranges of neutrino masses,mixing angle and so on. We
compare them to the experiment data
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