Phenomenology of String-Inspired Supersymmetric Unified Theories

超弦理论作为高维统一理论的候选者已经引起了人们的广泛关注。最近有许多尝试在更高维度的框架内解释超对称统一理论的各种问题。Yanagida和他的合作者已经证明了能够解决大统一理论中的三重态-二重态分裂问题的半统一模型可以很自然地嵌入到在轨道上紧致化的高维IIB型超引力中，并在这个框架下解释了模型的一些特征.他们还研究了通过轨道折叠破坏大统一群的六维模型。此外，还提出了三族夸克和轻子可能具有高维起源的猜想。除了这些研究，他们还研究了中微子振荡模型，宇宙中的leptogenesis，以及解释宇宙暗能量的模型。Yamaguchi和他的合作者提出了一种新的机制来解释额外维度框架中的三重态-二重态分裂和质子衰变的抑制。他们还研究了标准模型粒子可以达到的TeV尺度的额外维度。给出了目前的实验限制，并讨论了LHC实验中可能出现的信号。此外，他们还研究了超对称性破裂的调解机制和现象学后果。

Superstring theory has attracted much attention as a candidate for unified theory in higher dimensions. Recently there have been many attempts to explain various problems of supersymmetric unified theories in the framework of higher dimensions. Yanagida and his collaborators have shown that the semi-unification model which can solve the triplet-doublet splitting problem of grand unification can naturally be embedded into higher dimensional type IIB supergravity compactified on an orbifold, and some characteristic features of the model are accounted for in this framework. They have also studied six-dimensional models with grand unified group broken via orbifolding. Furthermore speculations have been given that three family of quarks and leptons may have higher dimensional origin. Besides these studies, they also investigated, e.g. models for neutrino oscillation, leptogenesis in the Universe, and a model to explain dark energy of the Universe. Yamaguchi and his collaborators have proposed a novel mechanism to explain the triplet-doublet splitting and the suppression of proton decay in the framework of extra dimensions. They have also investigated TeV scale extra dimensions accessible to standard model particles. Present experimental contraints are given and possible signatures at LHC experiment are discussed. Furthermore they studied mechanisms of mediation of supersymmetry breakdown and phenomenological consequences.