ABSTRACT
Chiral symmetry is spontaneously broken as a dynamical effect – presumably, from today’s perspective, as a property of the QCD interactions. Some remarkable connections between weak- and strong-interaction parameters can be established, such as the Goldberger–Treiman relation and the Adler–Weisberger relation. It turns out that the dynamics of the Goldstone modes, and their interactions with other hadrons such as nucleons, are strongly constrained by the underlying chiral symmetry of QCD; indeed, surprisingly detailed effective theories have been developed, which provide a very successful description of the low energy dynamics of the Goldstone degrees of freedom. This chapter introduces the subject of chiral anomalies. Nambu with other collaborators showed how the amplitudes for the emission of a single ‘soft’ (nearly massless, low momentum) pion could be calculated, for various processes.
