BCS, Nambu-Jona-Lasinio, and Han-Nambu -- A sketch of Nambu's works in 1960-1965

TL;DR

This paper reviews Yoichiro Nambu's groundbreaking work from 1960-1965, including reformulations of BCS theory, models of spontaneous symmetry breaking, and the development of quark models with non-Abelian gauge theories.

Contribution

It provides a chronological overview of Nambu's pioneering contributions to particle physics, highlighting the development of key theories and models during 1960-1965.

Findings

Reformulation of BCS theory emphasizing gauge invariance

Development of the Nambu-Jona-Lasinio model illustrating spontaneous symmetry breaking

Proposal of an alternative quark model with non-Abelian gluons

Abstract

The years of 1960-1965 were a remarkable period for Yoichiro Nambu. Starting with a reformulation of BCS theory with emphasis on gauge invariance, he recognized the realization of spontaneous chiral symmetry breaking in particle physics as is evidenced by the Goldberger-Treiman relation. A concrete model of Nambu and Jona-Lasinio illustrated the essence of the Nambu-Goldstone theorem and the idea of soft pions. After the proposal of the quark model by Gell-Mann, he together with Han constructed an alternative model of integrally charged quarks with possible non-Abelian gluons. All those remarkable works were performed during the years 1960-1965. Here I briefly review those works following the original papers of Nambu chronologically, together with a brief introduction to a formulation of Neother's theorem and Ward-Takahashi identities using path integrals. This article is mostly based on a lecture given at the Nambu Memorial Symposium held at Osaka City University in September 2015, where Nambu started his professional career.