Fixed-angle limits of multiparticle amplitudes

Abstract

Fixed-angle limits of multiparticle amplitudes are defined in terms of group variables. The behaviour of invariant variables in these limits is calculated. It is shown that exponential decrease of multiparticle amplitudes in certain limits is desirable to avoid the generation of non-Regge multiangular-momentum singularities due to the presence of physical-region poles in multiparticle amplitudes. These limits are then shown to be precisely the fixed-angle limits. Possible generalizations to production amplitudes of the Orear and Krisch phenomenological fits to the fixed-angle behaviour of the four-particle amplitude are also discussed.