Research of Superstring

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The research results of this project for 3 years from 1990 to 1992 are over many fields as seen in the Report of Research Results. So here we restrict ourselves to mentioning only to the main ones among them.1. Concerning String Field Theory, Hata proposed a method for determining the quantum action satisfying both unitarity and BRS invariance. He also proved for the first time that the pregeometrical string field theory indeed possesses the general coordinate invariance. Kugo et.al. clarified that the target-space duality as a particular property of string is in fact contained in the gauge invariance of the string field theory.2. There appeared a great progress in the non-perturbative approach to strings, in particular in the matrix model for the string in 1 or less dimensions. Yoneya and his collaborator succeeded in formulating 2-dimensional quantum gravity based on the minimal action principle. Sugamoto et.al. studied an evolution equation in the string field theory. As for the structure of string theory, Sakamoto made a remarkable finding that the string theories on a torus and on an orbifold are in fact equivalent.3. Research from the aspect of quantum gravity is also done actively. Sugamoto and his collaborators constructed and studied a topological Einstein gravity theory. Nakanishi and Abe developed a new method for solving quantum gravity in the operator formalism, and gave an exact solution to the 2-dimensional case by applying it.4. As for applications of string theory to unified models of elementary particles, Matsuoka and his collaborators studied Yukawa coupling constants and Kobayashi-Maskawa matrix in some models compactified on Calabi-Yao manifold. Otubo et.al. studied in detail the Yukawa couplings and the symmetry breaking Wilson-lines in Z_N and Z_N X Z_N orbifolds.