ABSTRACT
So far in this book we have worked with a rather limited class of quantum fields and interactions, restricting our attention to scalar field theories, Yukawa theory, and Quantum Electrodynamics. It is hardly surprising that these theories are not sufficient to describe all of the known interactions of elementary particles. But what other theories are possible, given that the Lagrangian of a renormalizable theory can contain no terms of mass dimension higher than 4?
