ABSTRACT
The idea of gauge invariance was introduced in Ch. 5, where it was shown that the interactions of QED, or quantum electrodynamics, arise out of the requirement of the symmetry of the Lagrangian under a local U(1) transformation. One can ask whether the same idea can be extended to other groups. Yang and Mills showed that it can be done, and we discuss the general structure of the resulting theories in this chapter. In some of the later chapters, we will see that this idea is crucial in understanding the dynamics of strong and weak interactions.
