UNITARITY EQUATION AT HIGH ENERGY

It is shown that in terms of the Sudakov variables the high-energy form of the unitarity equation is exceedingly simple. The result is used to derive the multi-Regge model contribution to the imaginary part of the two-body elastic amplitude. It is argued self-consistently that this contribution need not break the Froissart bound. The Sudakov technique is also shown to give immediate calculations of the ladder diagrams in perturbation theory and of n-fold, two-particle s-channel iterations of t-channel Regge poles. The latter leads to a simple derivation of the properties of the associated Regge cuts. © 1969 Società Italiana di Fisica.