Study of compactification in superstring and low energy effective theories theory

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Phehomenological features of supersymmetric models derived as the low energy effective theory of superstring have been studied from various points of view. Main results obtained in this project are followings.1. Supersymmetric models with an extra U(l) symmetry and a gauge singlet field can solve a μ-problem in the minimal supersymmetric standard model (MSSM). In this kind of models a μ term is generated effectively through an interaction between the gauge singlet field and ordinary Higgs fields and as its result the upper mass bound of the lightest neutral Higgs field can be larger than the one of the MSSM. We have estimated this upper bound taking account of the radiative symmetry breaking and various phenomenological constraints. We have shown that tan β < 2 region has not been excluded still now in these models.2. If the R-parity violating ε term is small enough, we can generate the neutrino masses without causing any contradiction with other phenomenological constraints. If we sup … More pose the existence of both an extra U(1) at an TeV region and the ε term, the neutrino masses can be generated due to the neutrino-gaugino mixings. We have shown that this mass generation scenario can easily realize the bi-large mixings in the lepton sector. We have extended this scenario so that the mass eigenvalues and flavor mixings in the quark sector are also explained in a unified way. A concrete model has been proposed in this direction. Additionally we have suggested that the smallness of both μ and ε terms can be explained if we suppose the MSSM contents couple with the superconformal field theory which can realize the large anomalous dimension.3. The D term inflation scenario based on the anomalous U(1) symmetry has been suggested to contradict with the density perturbation obtained by COBE. In order to solve this problem we have extended the model in such a way that both the μ problem and the smallness of neutrino masses can be explained and we have presented a concrete model. We have also studied the leptogenesis scenario in this type of models. Less