Yoichiro Nambu


I didn’t find out until I got back home that Yoichiro Nambu died about 2 weeks ago.  Such things don’t make the news, because who in hell is Yoichiro Nambu?  On the pretty good off-chance that you’ve never heard of him, keep reading.

While studying the Bardeen-Cooper-Schrieffer (BCS) explanation of superconductivity using Cooper bosons, Nambu noticed that they have a scalar gauge-invariant field with spontaneously broken symmetry, giving rise to another boson, this time massless with spin 0.  He published this in 1960.  Jeffery Goldstone continued this work and in 1964, generalized the results to quantum field theory with Abdus Salam and Steven Weinberg.  (In case you haven’t heard of those last two, they applied this work to Yang-Mills fields, explaining the electro-weak force, and they won the Nobel Prize in 1979 for their efforts.)  For Goldstone’s part, the bosons whose symmetry is broken are now called Nambu-Goldstone bosons.

If you’re thinking, “Gee, those massless spin-0 bosons whose symmetry is spontaneously broken sure sound familiar”, they should.  Also in 1964, Brout and Englert, Higgs, and Guralnik, Hagen, and Kibble noticed that spontaneous symmetry breaking in gauge fields for Nambu-Goldstone bosons causes the particles they act on to acquire mass.  Only one of those six people who discovered that mechanism is remembered today as the discoverer of the Higgs boson, and only Englert and Higgs got the Nobel Prize for it.

Kobayashi and Maskawa went on to show that spontaneous symmetry breaking predicts at least three families of quarks (top/bottom, charm/strange, and up/down).  Finally, we return to Nambu.  He and the previous two physicists won the 2008 Nobel Prize in physics for their work in spontaneous symmetry breaking.  Although Nambu was American and did most of his work at the University of Chicago, I suspect the reason he isn’t more widely known here is that his name doesn’t sound American enough.  This single discovery impacted research in strong, electro-weak, and gravitation theory.

He had an unusual career, being appointed associate professor at Osaka City University in 1949, being promoted to full professor in 1950, and finally earning his doctorate in 1952, at which time he went to the Institute for Advanced Study at Princeton (where Einstein was working), and at last, he moved to the University of Chicago in 1954, where he made professor in 1958.

Nambu also proposed that quark color mediated the strong force keeping quarks together.  This allowed Gell-Mann to create gluons in 1962, ushering in quantum chromodynamics.  Gluons, however, are vector bosons, having spin 1 and mass 0.

Dual resonance in particle physics refers to equality of amplitudes for s-channel and t-channel meson scattering.  Nambu in 1968 and Nielsen and Susskind in 1969 found an interpretation of this as infinitely many simple harmonic oscillators describing motion of a one-dimensional object.  In other words, they invented string theory.

That’s a pretty good field record for an American completely ignored by the American media.

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