Analysis of the non-perturbative structure of string theory on the basis of string field theory

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The purpose of the present research project is to study the various non-perturbative aspects in sting theory using "string field theory", which is a formulation of string theory, and also to reconsider the formulation of string field theory itself. We carried out the following researches for the two kinds of string field theory, Cubic String Field Theory (CSFT) and Vacuum String Field Theory (VSFT):(1)Analysis of time-dependent solutions in CSFTCSF is a string field theory expanded around an unstable D-brane. We studied the behavior of time-dependent solutions which express the decay process of the D-brane. String field theory differs very much from ordinary field theories in that the former contains infinite derivatives with respect to the time-coordinate. Our analysis is important for understanding properties particular to string field theory.(2)Construction and analysis of time-dependent solutions in VSFTWe constructed and studied time-dependent solutions corresponding to the decay … More of an unstable D-brane in the framework of VSFT, which is a string field theory expanded around the configuration without D-branes. Via the analysis using, in particular, Monte Carlo simulations, we found that it is very likely that solutions with desirable profiles exist(3)Analysis of the various properties of VSFT around a D-brane classical solutionWe studied (i) whether the gauge invariance structure associated with the photon state, and (ii) how the open string boundary condition is realiezed, in VSFT expanded around the D-brane solution.(4)Study of the relation between the loop equation in 4-dimensional N=4 super Yang-Mills theory and string field equation on AdS_5×S^5Four-dimensional N=4 super Yang-Mills theory and superstring theory on AdS_5×S^5 space-time are believed to be equivalent to each other (AdS/CFT correspondence). This research is a step toward the proof of the equivalence by showing that the loop equation in super Yang-Mills theory obeyed by the Wilson loop can be regarded as the equation of motion of superstring field theory. Although this subject was not contained in the original research plan, I think this is an important next stage of the present project. Less