Landau singularities in multi-Regge theory and fixed-angel behaviour

Abstract

A study of the implications of the Landau singularity structure in multi-Regge theory is begun. The incorporation of a physical-region pole in the three-Reggeon description of the six-particle amplitude is considered. Triple-Regge limits are found to involve fixed-angle limits of the four-particle amplitudes appearing in the residue of the pole. It is shown that under certain conditions the presence of the physical-region pole necessitates an « undesirable » set of angular-nmmeutum singularities of the forml1+l2+l3 = const. Exponential decrease of thc four-particle amplitude at fixed angle is then considered and it is shown that some examples of such behaviour including those most favoured by experimental results, do not necessitate these singularities.