Phenomenology of String-Inspired Supersymmetric Unified Theories

超弦理论作为高维统一理论的候选理论引起了人们的广泛关注。近年来，人们尝试在高维的框架下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，可以解决大统一的三重-双重分裂问题的半统一模型可以自然地嵌入到轨道上紧化的高维IIB型超重力中，并在这个框架中解释了模型的一些特征。他们还研究了六维模型，其中大统一群通过轨道折叠破碎。此外，还提出了夸克和轻子三族可能具有更高维度起源的推测。除了这些研究之外，他们还研究了中微子振荡模型，宇宙中的轻生模型，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三重重态分裂和在额外维度框架中抑制质子衰变。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。给出了目前的实验约束条件，并讨论了大型强子对撞机实验中可能出现的特征。此外，他们还研究了超对称破缺的中介机制和现象学结果。

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.