Yoshio Koide

is a Japanese theoretical physicist specializing in particle physics. He is best known for the Koide formula, a relation among the masses of charged leptons that has attracted attention for its surprising accuracy. While some physicists regard the formula as potentially significant, others consider it to be a numerical coincidence.

Early life and education Koide received a B.Sc. in physics in 1967 from Kanazawa University, followed by an M.Sc. in theoretical elementary particle physics at the same institution later that year. In 1970, he was awarded a Doctor of Science degree from Hiroshima University for his thesis “On the Two-Body Bound State Problem of Dirac Particles.”

Career After working as a postdoc in the physics department of Hiroshima University and then a postdoc in the applied mathematics department of Osaka University, he became, from 1972 to 1973, a Lecturer in the School of Science and Engineering, Kinki University, Osaka. Koide was Assistant Professor (1973-1977) then Associate Professor (1977-1987) of General Education, Shizuoka Women's University, Shizuoka. From April 1987 to March 2007 he was a Professor of Physics at University of Shizuoka, Shizuoka and then retired as professor emeritus. In 1986 he was a visiting professor at the University of Maryland and in 2002 a visiting researcher at CERN. Koide was from April 2007 to March 2009, a guest professor at Research Institute for Higher Education and Practice, Osaka University, then from April 2009 to March 2011 a guest professor and from April 2011 a guest researcher at Osaka University, and from April 2010 a professor, Department of Maskawa Institute, Kyoto Sangyo University, Kyoto.

Contributions to physics In the composite model of mesons, Koide's thesis demonstrated that a mass of a composite particle which consists of the rest masses cannot be lighter than except for the case when JP is not = 0-. This offered a severe problem for the quark model. (Koide’s work was done before the establishment of QCD.)

He published the famous Koide formula in 1982 with a different presentation in 1983.

Originally, Koide's proposed charged lepton mass formula was based on a composite model of quarks and leptons. In a 1990 paper, from the standpoint that the charged leptons are elementary, by introducing a scalar boson with (octet + singlet) of a family symmetry U(3), Koide re-derived the charged lepton mass formula from minimizing conditions for the scalar potential.

In 2009, he related the neutrino mixing matrix to the up-quark mass matrix. Koide and Hiroyuki Nishiura have published articles on a quark and lepton mass matrix model and a neutrino mass matrix model.