Duality in String Field Theory

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The string duality has played important roles in the studies of non-perturbative structures of superstring theory. The present research project aims at understanding this string duality in the framework of string field theory, and at the same time, completing the construction of string field theory on the basis of duality. Concerning the treatment of D-brane, which is the basic object for the duality structure of string theory, we have obtained a rather satisfactory results. However, much still remains to be clarified for the complete treatment duality structure using string field theory. As for other works concerning string duality, we have accomplished a number of satisfactory researches. The following is the concrete description of our researches.1) D-branes in Closed String Field Theory : We have introduced the D-brane degrees of freedom into closed string field theory. By demanding the closed string gauge invariance, we have succeeded in determining the dependence of the boundary state on the D-brane variable FィイD2μνィエD2 and the form of the kinetic term of FィイD2μνィエD2.2) Construction of 1/4 BPS Solutions in Super Yang-Mills Theories : String junction is a configuration of strings where the three strings emerging from three parallel D3-branes meet at a point. We have succeeded in constructing classical solutions in supersymmetric Yang-Mills theory which describes this string junction configuration.3) Analysis of Conformal Symmetries in Matrix Model : It was known that the conformal symmetry in AdS space-time emerges from super Yang-Mills theory as a quantum effect. We have presented a complete analysis of this quantum conformal symmetry beyond the Eikonal approximation.4) Construction of Classical Solutions in Super Yang-Mills Theory in Non-Commutative Space : We have constructed monopole and string junction classical solutions in supersymmetric Yang-Mills theory in non-commutative space where the coordinates do not com-mute each other.