Once again, I'm not sure I understand today's selection of Nambu together with Kobayashi and Maskawa. All are deserving theoreticians. K-M generalized the flavor mixing matrix of Cabibbo to 3 flavors and thereby introduced the likely origin of (thus far observed) CP violation.
But what is the justification of the Nambu prize? If it is for spontaneous symmetry breaking shouldn't people like Goldstone, Higgs, Englert, Brout, etc. also share the prize? The citation says
...for the discovery of the mechanism of spontaneous broken symmetry in subatomic physics.
If by mechanism they mean the general phenomena of spontaneous symmetry breaking then surely others deserve credit as well. If by mechanism they mean the actual dynamics, then I can only conclude they are giving the prize for the Nambu-Jona-Lasinio model? (Which is clearly not deserving of the prize!)
I think a more appropriate choice would have been Cabibbo-Kobayashi-Maskawa (Cabbibo is still alive) and Nambu-Goldstone + other.
Note added: I take back my comment about Cabibbo. The prize citation for KM is really for CP violation, and Cabibbo played no role in that. Regarding Nambu, the citation focuses on his being the first to discuss spontaneous symmetry breaking in a field theoretic context (not exactly Nobel worthy, in my view), and being the first to guess that the strong interactions exhibit spontaneous symmetry breaking, making an analogy with a conventional superconductor. This analogy is fleshed out in a talk given at Purdue in 1960, one year before Goldstone's scalar model which explicitly realizes what has now become known as a Nambu-Goldstone boson. Probably Nambu was the first person to deeply understand that the strong interaction (QCD) ground state spontaneously breaks axial symmetries -- I suppose that is by itself worthy of the prize.
See this Nobel committee scientific report for more details. Thanks to reader MFA for the pointer!