Gauge theories of weak interactions II (Circa 1981–1982 C.E.)

Abstract

This article is a sequel to “Gauge Theories of Weak Interactions (Circa 1973–1974)”, published in the Annual Review of Nuclear Science. Our purpose is to survey the state of the art eight years after; we have spared no effort, however, to make this article self-contained, comprehensible with only an occasional reference to the previous review. The tone of our presentation is set, and the scope of the discussion is delineated, by introductory remarks which emphasize some open questions in the field. We then proceed to examine the known structure of weak interactions in the light of the theory — now established, at least as a consistent description of electroweak effects in the low-energy domain — associated with the names of Glashow, Salam and and Weinberg and commonly referred to as Quantum Flavordynamics (QFD). Here, as well as later in the paper, we try to recapture the spirit of some of the original contributions by using judiciously-defined parameters which afford a model-independent perspective of the experimental data, particularly in situations where we suspect that theoretical fine structure may be hidden in the errors. The phenomenology provides a convenient starting point for discussing the underlying theory. We review briefly the methodology of spontaneously broken gauge theories, in the canonical framework with elementary spin-0 fields injected into the Lagrangian, and its application to the SU(3) C⊗SU(2) L⊗U(1) based standard model of quark-lepton interactions. Calculations of loop-level effects are described both in the context of the standard model and of SU(5)-based grand unification; specially emphasized is our contention that the renormalizability of the theory plays a crucial role in its ability to reproduce physical reality. At this point we deviate from the beaten path of orthodoxy to explore new directions in which weak-interaction theory might conceivably go. The principal motivation lies in our desire to avoid getting trapped in a no-new-physics desert in the energy interval 10 2 GeV-10 14GeV. Under the heading “extensions of standard QFD” we consider possible ways of making the desert bloom, which are tied to the canonical methodology; mentioned here are QFD models which survived the discovery in 1978, of parity nonconservation in the electron proton interaction; also mentioned are a few models that did not survive but which appear to be resurrectable by simple adjustment of the Higgs sector. More radical possibilities are considered in the penultimate section, on “generalizations of QFD”, where we present a critical review of recent theoretical speculations about dynamical symmetry breaking, composite models of quarks and leptons and the status of QFD as a fundamental theory. We conclude with a catalogue of unsolved problems and an appraisal of the outlook.