The development of our present understanding of the weak and electromagnetic interactions, and of their unification, has proven to be a fascinating dialogue between profound theoretical insights and remarkable experimental discoveries. The electromagnetic and weak interactions appear to be describable by local gauge theories. Phenomena involving charged leptons and photons can be described, to impressive precision, by the relativistic field theory of Quantum Electrodynamics. The incorporation of weak phenomena led, eventually, to the Glashow–Salam–Weinberg model, the so-called standard model. This theory describes the electroweak properties of leptons and quarks, and successfully predicted the existence of the massive W± and Z0 vector bosons. At present, the standard model is compatible with all well established experimental data, amassed by some tens of thousands of man-years of effort. This is an impressive state of affairs.

This book has its origins in a course of lectures given to first-year postgraduate students (mainly experimentalists) in high energy physics in Oxford. An elementary knowledge of high energy particle physics, together with the basic ideas of quantum mechanics and relativity, is assumed. However, these topics, in as far as they are required for later use, are reviewed in Chapters 1 and 2. An introduction to group theories and symmetries, concepts of great importance in particle physics, is also given in Chapter 2. In Chapter 3, the single particle wave equations for spin 0, spin ½ and spin 1 particles are developed, and an introduction to some of the concepts of field theory is given.