ABSTRACT
At the end of Ch. 14, we commented that it is necessary to have massive vector particles in order to describe weak interactions. We also commented that without a gauge symmetry, a theory with a massive vector boson is not renormalizable. On the other hand, gauge theory precludes any mass term for gauge bosons. The way out of this apparent impasse was sought through spontaneously broken gauge theories: a gauge symmetry would ensure renormalizability, but it would be broken spontaneously so that the gauge bosons would be massive. The idea was successfully employed by Weinberg and Salam in 1967-68, and ’t Hooft proved the renormalizability of such models in 1971. The model that grew out of these ideas is now known as the standard electroweak model , because it described both weak and electromagnetic interactions. Along with the theory of strong interactions in the form of quantum chromodynamics or QCD, it provides the standard model of all particle interactions except gravity. In this chapter, we will describe the standard electroweak theory in the form that it was originally proposed — involving only the leptons and considering neutrinos to be massless. Quarks will be accommodated in this theory in Ch. 17, and the question of neutrino mass will be discussed in Ch. 22.
