The role of gauge theory, symmetry-breaking, and electroweak unification in the discovery of weak neutral currents

Abstract

The three historical and logically independent components of the Electroweak Standard Model are the exact chiral gauge theory of weak interactions, the Higgs mechanism for spontaneous symmetry‐breaking, and electroweak mixing. I put into historical perspective my 1958 invention of the first gauge theory of weak interactions, predicting weak neutral currents, and show how the fundamental differences between global and gauge symmetries and between partial and exact symmetries gradually emerged. Only renormalizability is necessary for theoretical consistency; electroweak mixing is logically independent. This extra ‘‘unification condition’’ distinguishes a unified theory, even in the sin2θW→0 limit, from a pure SU(2)W gauge theory of weak interactions. In the low‐energy effective theory, the effects of unification turn out to be small (<11%). Nevertheless, historically the mixing sin2 θW∼0.3 observed in the first weak neutral current experiments gave circumstantial support for the Standard Model and targeted the search for W‐ and Z‐bosons.