Diffraction scattering of hadrons: The theoretical outlook

This is a review of the salient features of high energy diffraction scattering of hadrons. It begins with a summary of the experimental situation for those processes which persist at very high energies—the diffractive processess—and defines the underlying exchange mechanism called the Pomeron. A review is made of the key features of the multiperipheral model, since it lies at the beginning of all studies of diffraction. Its virtues and blemishes are exposed. Then we turn to various models which attempt to add unitarity to the multiperipheral model. From the point of view of the direct channel we consider absorptive models, eikonal models, and the multiperipheral bootstrap. The $t$ channel is taken next, and an exposition of the formulation and major results of Reggeon field theory is given. "Et fut une digne parole de Julius Brusus aux ouvriers qui lui offraient pour trois mille écus mettre sa maison en tel point que ses voisins n'y auraient plus la vue qu'ils y avaient: `Je vous en donnerai,' dit-il, `six mille, et faites que chacun y voie de toutes parts.' " de Montaigne, M. (1585-88), "Du repentir"