Study of Unified Theory of Elementary Particles Based on Supergravity

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This research attempted to clarify the structure of supergravity as a unified theory of particle physics, based on the recent theoretical and experimental progress, through phenomenological consistencies. The main attainment is that the characteristic features realized in particle physics, such as a stability of nucleons, generation structure of quarks and leptons, their hierarchical masses and the suppression of flavor-nonconserving neutral current processes, can be understood as the reflection of the horizontal symmetry of generations, which governs, in supergravity, the structure of superpotential and Kaelar potential in a specific way. Especially, the horizontal symmetry based on noncompact group SU(1,1) allows us to understand universally all of the violations of the fundamental symmetries of parity, charge conjugation and time reversal, as a spontaneous breakdown of the horizontal symmetry. The minimal supersymmetric standard model is extended in a vectorlike manner with the infinite-dimensional unitary representations of SU(1,1), and chiral structure of quarks and leptons, and their hierarchical Yukawa interactions are realized through the spontaneous breakdown of SU(1,1). The further extension of this minimal model to the noncompact grand unified group, which combines SU(1,1) with SU(3)*SU(2)*U(1), gives unified view on the relation among low energy gauge symmetry, chiral massless spectra and their gauge quantum numbers. It is also strongly suggested that behind the vectorlike horizontal symmetry, whose spontaneous breakdown realizes the chiral world, exists the extended supersymmetry due to supergravity with N*2. Since the extended supersymmetry severely restricts the structure of superpotential and Kaeler potential, future attempts along this direction will give great progress in the unified theory of particle physics based on supergravity.