| Summary: | 博士 === 國立臺灣大學 === 物理研究所 === 100 === The standard model (SM), which describes the gauge group SU(3)_C×SU(2)_L×U(1)_Y related to strong interaction, weak theory and electromagnetic interaction, explains most of the phenomena in the nature. However, there remain some problems which can not be explained by the SM, such as the the origin of CP violation, the baryon asymmetry of the universe, the hierarchy problem related to the weak scale and Plank scale, the strong CP problem, the light neutrino mass, and the number of fermion generations. In this thesis I will focus on three of these problems, which are
listed as follows.
1. The topic related to the source of CP violation. In order to explain the source of CP violation we introduced a multi-Higgs model with nonzero spontaneous CP violating phase, and regarded the phase, which is assumed to be identical in magnitude to the phases in quark mixing matrices, as the source of CP violation. This assumption will lead to some simpler Yukawa coupling matrices. We also applied the idea to the lepton sector. The Jarlskog invariant in PMNS matrix can be predicted, which can be used to distinguish different models we take.
2. The topic related to the light neutrino mass and Higgs decay in seesaw models. The seesaw mechanism, involving right-handed neutrinos with very large Majorana mass, explains the light neutrino masses successfully. But the too
huge mass of the heavy neutrino and the too tiny coupling with this heavy neutrino the other particles cause the difficulty in verifying the seesaw mechanism. We investigated the effect on Higgs decay in some seesaw models with large heavy-light mixing, which can increase more than 20% than that in the SM. The subsequent four body decays are also different from the prediction in SM.
3. The topic related to the lepton flavor violation in SM with four fermion generations. The SM with more than three generations, e.g., with four generations, is also a possible candidate. We studied the lepton flavor violating process
such as μ-e conversion in atoms in the SM with sequential four generations. We found that the current experimental bound on μ-e conversion with Au constrains the relevant coupling constant most stringently. The experiment on
μ-e conversion in Ti will lead to the most stringent constraint in the future.
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