Spontaneous Symmetry Breaking in Particle Physics

Abstract

AbstractI will review the appearance of spontaneous symmetry breaking (SSB) in particle physics at the end of the fifties and beginning of the sixties of the XXth century. I will recall Heisenberg non-linear spinor theory and the genesis of the first model (NJL) of fermion mass generation developed in collaboration with Yoichiro Nambu, based on the idea of spontaneous symmetry breaking. Both the non-linear spinor theory and the NJL model are invariant under a chiral transformation ($$\gamma _5$$ γ 5 —invariance) which was introduced by Bruno Touschek in 1957 and named by Heisenberg the Touschek transformation. Then I will briefly describe the subsequent evolution where the NJL model became an effective theory for low energy QCD and SSB was the key for the electroweak unification. Finally I will consider SSB in non-equilibrium which may be of interest in cosmology.