Researcher Information



Challenge the mystery of the universe and the world of elementary particles

Department of Physics, Nonlinear Physics

Fieldparticle physics, cosmology
Keywordsuperstring theory, standard model of particle physics, cosmology, compact space

Introduction of Research

Superstring theory is a good candidate for a unified theory of all interactions including gravity, and quarks and leptons as well as the Higgs particle. We study particle physics and cosmology, which can derived from superstring theory. Superstring theory predicts six-dimensional space, which must be compact, in addition to our four-dimensional spacetime. Geometrical aspects of compact space determine which type of particle appears and their properties. We study superstring theory on compact space, which realizes our world and derive their predictions.

Representative Achievements

Y.Katsuki, Y.Kawamura, T.Kobayashi, N.Ohtsubo, Y.Ono and K.Tanioka,
''Z(n) Orbifold Models,''
Nucl. Phys. B 341, 611 (1990).
T.Kobayashi, S.Raby and R.J.Zhang,
''Searching for realistic 4d string models with a Pati-Salam symmetry: Orbifold grand unified theories from heterotic string compactification on a Z(6) orbifold,''
Nucl. Phys. B 704, 3 (2005)
K.Choi, K.S.Jeong, T.Kobayashi and K.i.Okumura,
''Little SUSY hierarchy in mixed modulus-anomaly mediation,''
Phys. Lett. B 633, 355 (2006)
T.Kobayashi, H.P.Nilles, F.Ploger, S.Raby and M.Ratz,
''Stringy origin of non-Abelian discrete flavor symmetries,''
Nucl. Phys. B 768, 135 (2007)
H.Ishimori, T.Kobayashi, H.Ohki, Y.Shimizu, H.Okada and M.Tanimoto,
''Non-Abelian Discrete Symmetries in Particle Physics,''
Prog. Theor. Phys. Suppl. 183, 1 (2010)

Department of Physics, Nonlinear Physics



What is the research theme that you are currently focusing on?

I have been studying particle physics and cosmology within the framework of superstring theory. There are various elementary particles and they have different properties such as different charges and different masses. There are also four interactions among particles such as gravitational interaction, electromagnetic interaction, weak interaction and strong interaction. Their origin is assumed to be one-dimensional object, i.e. string in superstring theory. Superstring theory predicts six-dimensional compact space in addition to our four-dimensional spacetime. Strings can have various states in such a compact space, e.g. different momenta and winding numbers. That can correspond to various properties of particles and interactions. Particle properties depend on geometrical aspects of compact space, although we do not know which compact space is realized. I have been studying how particle properties appear from geometrical aspects of compact space and which compact space is realistic to derive our world.

What made you decide to become a researcher?

My story is not so dramatic. I was just a boy, who liked math. I entered the Department of Physics. I was not satisfied after learning Physics for four years. Then, I went to graduate school. I studied for another five years, however, I was not satisfied and wanted to study more. I was not “ambitious”, nor did I have confidence that I could become a professor. I was just unsatisfied and wanted to study more. I studied in several institutes as a postdoctoral fellow. Then, I may have become a researcher, just thinking “I am not satisfied yet. Another step ahead, another step higher”.

What do you usually do when you get stuck in your research?

We may get stuck in several situations, such as (i) an extension to a new direction, and (ii) an unsolved problem in research. I never got stuck in the former case. I have many collaborators including students. If I have a faint idea, I usually talk to them about it. My ideas are often faint and unclear. So, I may be a noisy guy to them. However, they are very kind. We discuss. They also give me some new ideas, which are better than mine. Such discussions show a new direction to study, although the initial ideas are faint.

When I get stuck in the latter situation, I just leave it. I remember it in the back of my mind and wait for a breakthrough to come to me. It would occur when I am walking or I am in bed. Today, I am again walking around the beautiful campus of Hokkaido University with a difficult face or a faint smile.

Please tell us about yourself; things you are good at, your favorites, hobbies, and daily routines.

I love beer. I have liked it since I was a student, but one of important turning points was that I stayed in Munich as a postdoctoral fellow in Ludwig Maximilians University (the University of Munich). Nowadays, craft beer becomes well known even in Japan, but at that time only the beers from major companies were on the market in Japan. On the other hand, in Germany each city has several breweries and they brew unique Bier(beer) suited to the climate. I felt a difference even for beer. Also I had valuable experience there. My experience and talks with friends at that time underlie my way of looking at things and thinking. I miss the Bier I had in the European summer…“Ein Helles bitte”.