Introduction

In chapter 3 we showed how Regge trajectories could be generated by the imposition of unitarity on the basic exchange force, whether that force was a non-relativistic potential, a single-particle-exchange Feynman diagram in a field theory, or even a single Reggeon-exchange force in a bootstrap model. But the various bootstrap methods which we reviewed in section 3.5 all suffered from the very serious defect that they were limited to two-body unitarity in one channel or another. In chapters 9 and 10 we have found that Regge theory can also predict successfully the sort of behaviour to be expected in many-particle scattering amplitudes, so it is now possible to return to some of the most fundamental questions of Regge theory, such as how the Regge singularities are self-consistent under unitarity, and whether the bootstrap idea introduced in section 2.8 can be correct.

For this purpose we need models for many-particle production processes, and in the next two sections we examine two such models. One, the diffraction model, though inadequate by itself, does describe Pomeron-exchange effects and the fragmentation region, while the other, the multi-peripheral model, though applicable only in certain regions of phase space, allows one to approximate the effect of multi-Reggeon exchange. The so-called ‘two-component model’ which incorporates both these contributions seems to account quite well for the basic structure of many-particle cross-sections, if not all the details.