Inflationary cosmology
The ultimate goal of this project is to clarify the birth, the evolutionand the nature of the Universe via the theory of fundamental physics. In the beginning of the Universe, the quantum effect of gravity may play an essential role and the energy-scale of the Universe is expected to have been very high, which cannot be attained by the ground-based experiments. Furthermore, the interactions between elementary particles were important, which governs the expansion of the Universe, and due to the vacuum energy of the elementary particles, it is thought that the Universe had experienced an accelerated expansion, referred to as the inflation. According to the inflationary scenario, the standard 'hot' Big-Bang universe was realized at the end of the inflation by the energy release of the vacuum energy and the Universe was subsequently filled with the thermalized hot plasmas. One of the most important aspects of the inflationary scenario is that the quantum fluctuation was generated during the inflation, which led to a seed of the density perturbation. It is widely believed that the large-scale structure of the Universe observed at present has been developed from such a tiny perturbation as a course of the gravitational evolution.
Revealing the early Universe by observations
For a complete understanding of the birth and the evolution of the Universe, a role of the elementary particle physics is crucial. Recent progress of the particle physics leads us to a more deeper insight into the fundamental aspects of the very early universe. The purpose of this project is to construct a consistent scenario for cosmic history from the early universe to the observed universe. In principle, the cosmological phenomena occurred at the early stage can affect the present day of the Universe. Thus, we can test the cosmic scenario based on the particle physics via the observation of the cosmic microwave background and that of the galaxy distribution. This is one of the important tasks in this project. Justification of the scenario for early universe is quite hard, however, recent development of the observations with a large telescope and a satellite experiment is gradually extending our view of the early Universe. Although indirectly, it is now possible to verify a fundamental theory of the birth and the evolution of the Universe.