Nambu and Kobayashi-Maskawa share the 2008 Nobel Prize for physics for their contributions to the understanding of symmetry breaking in particle physics. Nambu's contribution is on the spontaneous symmetry breaking which can occur in many situations such as standard model, supersymmetry and grand unified models. Kobayashi-Maskawa theory is concerned with the CP violation which shows up in the CKM matrix when the number of quark generation is 3 or more. B-factory experiments proved their theory is correct.
I happened to be a graduate student under the guidance of Professor Nambu in 1967-1970. It was the golden days of particle physics, and at the same time when Nambu formulated the famous string theory of hadrons. I wish to convey to the reader how Nambu reached the idea of string theory as I see it, and how he contributed to particle physics as one of the greatest physicists of today.
An intimate relationship between Nambu's accomplishments and the condensed-matter physics is reviewed, which comprises (i) Nambu's theory and the BCS theory for superconductivity, (ii) Nambu-Goldstone theorem and (iii) Nambu's theory and the Anderson-Higgs mechanism.
If we look back over the past half a century, we see that Japanese physicsists played major roles in spontaneous symmetry breaking, theory of CP violation, the construction of the B factory, and verifying the validity of the theory of CP violation. This is a set of historical achievements for which the Japanese Physical Society can be proud. I will take this opportunity to summarize this history.
Professor Maskawa spent 29 years in total in Kyoto University; 6 years of 1970-1976 as an assistant professor in Physics Department and 23 years of 1980-2003 as a professor at Yukawa Institute, a professor at Physics Department and the director of Yukawa Institute. I was near him for almost all period of those years. I will write many things about Prof. Maskawa in Kyoto University and his personality focusing mainly on the era in which the Kobayashi and Maskawa's work was performed.
The B factory at KEK has been operated successfully with updating world record of the luminosity of electron-positron colliders, and has provided experimental test to the Kobayashi-Maskawa model. First of all, large CP violation was discovered in B meson system, which is one of the predictions of the model, followed by its confirmation in various B meson decays. On the other hand, some phenomena have been found, which may not be fully explained by the model alone. It is strongly anticipated to clarify them by the upgraded B factory(ies).