Introduction

So far in this book we have been solely concerned with hadronic interactions, which are the principal field in which Regge theory has been used. We have ignored electromagnetic effects in assuming that isospin is an exact symmetry of the scattering processes, and have not needed to mention the weak-interaction properties of the particles such as β-decay, etc. But of course any discussion of the electromagnetic or weak interactions of hadrons necessarily involves consideration of their hadronic properties too, because it is the strong interaction which is mainly responsible for the composite structure of the hadrons. Regge theory has played a small but not insignificant role in the development of theories of these weaker interactions, and clearly if there is to be any chance of unifying all the interactions they must be reconciled with Regge theory. In this chapter we shall look rather briefly at the problems which may arise in so doing.

Basically there are two such problems. First, weak interactions (and from now on we shall usually use the word ‘weak’ to refer to both electromagnetism and the weak interaction) are generally formulated in terms of a Lagrangian field theory for the interaction of a basic set of elementary particles. These are the leptons, l (i.e. electron e, muon μ, and neutrinos ve, vμ), photon γ, vector boson W, etc., and elementary hadrons (which at least initially do not lie on Regge trajectories but occur as Kronecker δαJ terms in the J plane).