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Yoichiro Nambu, winner of the 2008 Nobel Prize in Physics, has died at age 94. He was one of perhaps a dozen or so physicists who can rightly be called a "founding father" of the Standard Model of particle physics.
He taught at the University of Chicago from 1954 to 1991 and was awarded U.S. citizenship in 1970. Prior to joining the faculty at the University of Chicago, he sent two years at the Institute for Advanced Studies in Princeton, and three years before that (prior to receiving his doctoral degree) as an associate professor at Osaka City University in Japan.
Nambu was awarded the Nobel prize "for the discovery of the mechanism of spontaneous broken symmetry in subatomic physics." He shared the prize with two Japanese scientists, Makoto Kobayashi and Toshihide Masukawa.His 1961 co-authorship of the Nambu–Jona-Lasinio model, an effective theory of nucleons and mesons that is now considered a low energy effective theory of quantum chromodynamics (a theory that did not exist at the time) is still used as a practical tool for making computations in QCD, and is one of a handful of leading means by which QCD is approximated in ways that are numerically tractable. This theory was one of the first to correctly determine that most of the mass of a proton or neutron arises from the self-interacting field of the proton with itself, rather than from the fermions itself. A 2006 QCD paper described this model as "one of the most successful efficient models in the QCD of light hadrons in the non-perturbation region." This model is frequently applied in the context of "Lattice QCD" which is a numerical approach to modeling QCD in the low energy non-perturbative ("infrared") regime. The main feature of QCD not included in the early versions of the model was "confinement" (i.e. the reality that quarks always appear confined in hadrons). A later version of the model called the Polyakov-Nambu-Jona-Lasinio model addressed this shortcoming.
As QCD developed he was the one to propose the concept of "color charge" which is one of the central concepts of QCD.
The massless bosons that arise in field theories with spontaneous symmetry breaking are sometimes referred to as Nambu–Goldstone bosons, although more often these days, this has been abbreviated to "Goldstone bosons". These bosons were discovered by Nambu, and then generalized to quantum field theory by Jeffrey Goldstone.
Italian QCD physicist Marco Frasca remarks that: "It is a severe loss for physics but his legacy will survive him forever." He also provides this historical footnote on Nambu and his colleague Jona-Lasinio:
Giovanni Jona-Lasinio is one of the greatest Italian physicists and it is well-known for his contributions to quantum field theory and statistical physics. . . . His model, postulated together with Yoichiro Nambu, represents the right behaviour of quantum chromodynamics at very low energies and put the basis for the future understanding of broken symmetries in particle physics. Indeed, Jona-Lasinio took the Nobel medal Giovanni Jona-Lasinio Nobel Lecture on behalf of Nambu and presented also the lecture. Nambu could not go to Stockholm and so, the award passed by the hands of Jona-Lasinio.Only a few of these "founding fathers" of the Standard Model are still living now, but many of today's leading physicists worked under them as they established their own careers in the field. We are only a single generation removed from the beginning of the truly modern, post-Standard Model, era of fundamental physics.