String field theory and D-brane

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We studied string field theory and the subcritical quantum gravity which is described by the matrix quantum mechanics. In particular, we focused on the open string sector where the D-brane plays the fundamental role. Matrix quantum mechanics is defined by the quantum mechanical system where matrix is used as the dynamical degree of freedom. So far, people have studied their closed string sector. These degree of freedom is known to be reduced to the free fermion and extensive study was possible for them. On the other hand, the open string which is related the D-brane is described by so called non-singlet sector. The system is then governed by the Calogero system with interactions. Because of this interaction, the analysis of the system becomes far more difficult and there have not been many studies. In order to treat this issue, in this study, we focused on the infinite set of conserved charges and succeeded to construct the states which diagonalize all the charges. In this way, we clarified the solvability of the open string sector which has not been so clear. We also studied M(embrane) theory in the 3 form flux background. This is a generalization of the string motion in the presence of two form flux. So far, this problem has been studied so called Nambu bracket. In this study, we have studied the motion of point like particle, which will spread when it moves in the flux. From this observation, we could define the vertex which describe the interaction of the particle. We also studied UV/IR mixing which was studied extensively in the noncommutative space to our background.