Yoshio Koide

Yoshio Koide (小出 義夫, Koide Yoshio, born May 16, 1942 in Kanazawa, Ishikawa) is a Japanese theoretical physicist working in particle physics. Koide is known for his eponymous Koide formula, which some physicists think has great importance but which other physicists contend is merely a numerical coincidence.

Koide earned in 1967 a B.Sc. with major in physics and in 1967 a M.Sc. in Theoretical Elementary Particle Physics from Kanazawa University. In 1970, he received his Doctor of Science degree from Hiroshima University with a thesis “On the Two-Body Bound State Problem of Dirac Particles”.^[1]

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.

In the composite model of mesons, Koide's thesis demonstrated that a mass ${\displaystyle m}$ of a composite particle which consists of the rest masses ${\displaystyle m_{1},m_{2}}$ cannot be lighter than ${\displaystyle {\frac {1}{2}}(m_{1}+m_{2})}$ except for the case ${\displaystyle m_{1}=m_{2}}$ when J^P is not = 0^-. This offered a severe problem for the quark model. (Koide’s work was done before the establishment of QCD.)^[1]

Katuya and Koide predicted that lifetimes of D^± and D⁰ should be considerably different from what was at that time the conventional anticipation tau(D^±)= tau(D⁰). Their prediction of these lifetimes was the first in the world prior to the experimental observation.^[2]

He published the famous Koide formula in 1982^[3] with a different presentation in 1983.^[4]

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.^[5]

In 2009, he related the neutrino mixing matrix to the up-quark mass matrix.^[6] Koide and Hiroyuki Nishiura have published articles on a quark and lepton mass matrix model^[7][8] and a neutrino mass matrix model.^[9]

• Koide's web site (in Japanese)
• physics papers by Y. Koide available on arxiv.org
• Scientific publications of Yoshio Koide on INSPIRE-HEP