I have been working on theoretical particle physics, broadly defined. Around the time I entered graduate school, there were a series of great discoveries, from neutrino oscillation with large mixing angles, non-zero dark energy to higher peaks of cosmic microwave background anisotropies. Those discoveries let me wonder if we can use theories more fundamental than the Standard Model of particle physics to understand those phenomena better. During the course of such a theoretical endeavor, I have had to face situations where I had to improve existing theories by myself. Consequently, my research interests include string duality and other mathematical aspects of string theory these days. My primary research topics may change over time. For experts, my personal web page will provide more up-to-date information.