The 2008 Nobel Prize for Physics has been awarded to three physicists whose insights help to explain fundamental properties of both the strong and the weak interactions. Half the prize goes to Yoichiro Nambu (University of Chicago) “for the discovery of the mechanism of spontaneous broken symmetry in subatomic physics.” Half will be shared by Makoto Kobayashi (High Energy Accelerator Research Organization Tsukuba, Japan) and Toshihide Maskawa (Yukawa Institute for Theoretical Physics, Kyoto University) “for the discovery of the origin of the broken symmetry which predicts the existence of at least three families of quarks in nature.”
Among Nambu’s key contributions was the realization, in the early 1960's, that the strong interactions exhibit spontaneously broken chiral symmetry, which can be used to understand both the existence of the light pion and the origin of the nucleon mass. Kobayashi and Maskawa’s most important contribution came more than a decade later, as the standard model was being constructed. They generalized the 2x2 quark mixing matrix that had been introduced by Cabibbo to the 3x3 case, thereby introducing an extra generation of quarks and showing how CP violation could enter naturally into the standard model.
“This year’s prize recognizes two theoretical pillars of our modern understanding of the fundamental constituents of matter and the forces that act on them,” explains APS Vice President Curtis Callan of Princeton University. “Nambu profoundly deepened our understanding of mass. His prescient work of the early 60s today allows us to explain how the proton and neutron (and, by extension, the atomic nucleus) can be made of nearly massless quark constituents and yet be very massive. Kobayashi and Maskawa developed a description of the intrinsic mass of the three generations of quarks which has been verified in spectacular experimental detail. It provides a framework for understanding why matter vastly dominates over anti-matter in our universe and also how neutrinos can change their character as they propagate to the Earth from the Sun.”
All three of the 2008 Laureates have previously been recognized by the APS with the J. J. Sakurai Prize for Theoretical Particle Physics (Kobayashi and Maskawa in 1985, and Nambu in 1994). Nambu also won the 1970 APS Dannie Heineman Prize for Mathematical Physics. Nambu’s initial papers leading to his portion of the prize in appeared in APS journals nearly fifty years ago.
“We are pleased that Nambu's work was published in Physical Review Letters
in 1960,” says APS Editor-in-Chief Gene Sprouse, “in the then-nascent journal’s second year of publication.” This article is freely available online. "Axial Vector Current Conservation in Weak Interactions"
In addition to his Nobel Prize winning work, Nambu was also one of the progenitors of string theory, having proposed the action for a relativistic bosonic string.