Phenomenological and cosmological aspects of string axion and supersymmetric standard models 弦理論アクシオンと超対称標準模型の現象論的かつ宇宙論的側面についての研究

Recent discoveries and insights depended on some experimental results have already deeply impacted our understanding. Although the standard model in particle physics is consistent with almost all the experimental results obtained so far, there also exist unsolvable problems, even in the cosmology. It suggests that our standard model should be extended, beyond from the electroweak scale to higher energy scale. It is the time that we have to solve these serious problems facing now using all the knowledge we have gained until now. In this thesis, we have studied these relational extended models by considering the following two approaches. First, we concentrate on the inflation models as a high energy physics in the early universe. So far, there are found many kinds of slow-roll inflation models, in this thesis, we pursue mainly inflation related to axion. Typically, the axions are particularly attractive inflation candidates because they have shift symmetry to all orders in perturbation theories. Motivated above a key ingredient, we have studied an axion inflation model recently proposed within the framework of type IIB superstring theory, where we pay particular attention to a sub-Planckian axion decay constant. Further, we study a general class of small-field axion inflations which are the mixture of polynomial and sinusoidal functions suggested by the natural and axion monodromy inflations. In such a case, the axion decay constants, leading to the successful axion inflations are severely constrained in order not to spoil the Big-Bang nucleosynthesis and overproduce the isocurvature perturbation originating from the QCD axion. We, in turn, find that the cosmological favorable axion decay constants are typical of order the grand unification scale or the string scale which is consistent with the prediction of closed string axions. Our axion potential can lead to the small field inflation with a small tensor-to-scalar ratio, and a typical reheating temperature can be as low as GeV. Second, we have concentrated on about the cosmology in the viewpoint of supersymmetry phenomenology. After we briefly review a few variations on the basic picture of the minimal supersymmetric standard model(MSSM) and its application to the cosmology, we consider domain walls in the Z3 symmetric Next-to-MSSM. The spontaneous Z3 discrete symmetry breaking produces domain walls, and the stable domain walls are problematic. Thus, we assume the Z3 symmetry is slightly, but explicitly broken and the domain walls decay. Such a decay causes a large late-time entropy production. We study its cosmological implications on unwanted relics such as moduli, gravitino, lightest supersymmetric particle(LSP) and axion. Moreover, we also propose an Affleck-Dine leptogenesis model with right-handed neutrino as a minimal extension of MSSM, which is based on LHu direction, and we have pointed out that sufficient amounts of baryon asymmetry can be generated in our model. Through this thesis, we hope that our scenario would clearly contribute to our understanding of the feature of the universe.

(主査) 教授 小林 達夫, 教授 鈴木 久男, 特任准教授 瀬戸 治, 講師 末廣 一彦

理学院（宇宙理学専攻）