Breaking and restoration of chiral symmetry

Chiral symmetry is a symmetry under combined γ5 and flavor transformations. Although the Yang-Mills equations were invented in 1954, chiral symmetry was first introduced in 1960 into the physics of nucleons and mesons, which the author shall describe as physics in the Nambu-Goldstone, or broken symmetry mode. Chiral symmetry is a strict symmetry underlying the Yang-Mills equation in the limit of zero bare (current) quark mass. In these lectures, the author shall consider only this limit, later talking a bit about explicit chiral symmetry breaking which is introduced by giving the quarks bare masses. 34 refs., 9 figs