study of nonperturbative aspects of superstring theory using string field theory

本研究的目的是克服“接触项问题”，这是超弦场理论所具有的发散问题，长期以来一直是理论形成的障碍。我们提出了一种新的正则化方案，在该方案中，时空维度的数量被移动到足够大的负值。我们主要在NSR形式中的轻锥规范超弦场理论的背景下验证了我们的正则化。我们已经证明，我们的正则化效果很好，至少对树级幅度是有效的。我们在多圈振幅的分析方面也取得了进展。除了这些分析之外，我们还追求了一种新的弦场理论公式，其中弦世界表被描述。我们还研究了宇宙学，特别是包括物质场的量子效应和反向反应。

The purpose of this research is to overcome the ``contact term problem", which is a divergence problem possessed by superstring field theory and has been an obstacle to the formulation of the theory for a long time. We proposed a novel regularization scheme in which the number of space-time dimensions are shifted to a sufficiently large negative value. We verified our regularization mainly in the context of the light-cone gauge superstring field theory in the NSR formalism. We have shown that our regularization works well at least for the tree-level amplitudes. We have made a progress also in the analysis of the multiloop amplitudes.In addition to these analyses, we have pursued a new formulation of string field theory in which the string worldsheet is discritized. We also have studied cosmology particularly including quantum effects and back-reaction of matter fields.