Research on time-dependent solutions and application to cosmology in superstring theories

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We have carried out research related to quantum gravity and its consequences, which is one of the greatest problems in elementary particle physics and gravity. Since the most promising candidate for such a theory, the superstring, is defined in higher dimensions, extra dimensions must be compactified in order to give a realistic description of our world. In this research, we have investigated time-dependent inflationary solutions systematically to obtain realistic models for our universe in the low-energy effective theory of superstring, and clarified the possibility of describing big-bang singularity quantum mechanically by using supersymmetric time-dependent solutions. We have also clarified some properties of higher-dimensional black holes related to superstring. We have also studied physical applications of these results to cosmology. Our results turn out to be very useful in clarifying the interplay between the fundamental theory of particle physics and cosmology. Our concrete res … More ults are as follows.1. We obtained interesting cosmological solutions systematically in the supergravity as an effective theory of superstring with higher order quantum corrections. These solutions clarify the possibility of explaining inflation at the early universe as well as current accelerating expansion.2. Supersymmetric solutions are one of the rare system in which we can study their quantum properties. We constructed such siolutions in supergravity and showed that they can be used to describe big-bang singularity in the early universe. We have also studied supersymmetric D2-brane system systematically and clarified their physical properties.3. It is known that most of the energy of our universe consists of dark matter and dark energy. We pointed out that it is natural that they interact with each other and obtained observational bound on it.We have also obtained some interesting new results on confinement in QCD by superstring and universality of the entropy-area relation for black holes. Less