Complex Angular Momentum Theory in Particle Physics

Abstract

AbstractA critical review of the techniques of complex angular momenta used at present in the Regge theory of strong interactions is presented. After discussing the kinematical singularities of helicity amplitudes, their crossing properties as well as the constraints they satisfy, the reggeization procedure for two‐body helicity amplitudes is reviewed in detail. The properties of the generalized Froissart‐Gribov continuation are investigated. The factorization properties of Regge pole contributions to a general two‐body scattering amplitude are studied and the various mechanisms producing the dip structure of differential cross‐sections are discussed. The complications of the reggeization for amplitudes describing unequal‐mass reactions at high energies in the forward direction are discussed and a survey of the status of “conspiracies” of singularities in the complex angular momentum plane is given. Both, the group theoretical and the analytical methods are discussed in treating the conspiracy problem. Finally, a review of the present situation is given regarding the influence of branch cuts in the complex angular momentum plane and their phenomenological consideration in various multiple scattering models. It is shown that the multiple scattering correction in the Glauber‐eikonal type of approach correspond to cuts in the angular momentum plane which represent absorptive corrections to the single Regge exchanges. It is clear from this discussion that cuts in the complex j‐plane, describing multi‐Regge pole exchanges, cannot be neglected.