PREDICTIONS FOR gg ?? pp: WHAT PHOTONS AT DAFNE WILL SEE

The aim of this article is threefold. Firstly, to discuss briefly why two photon interactions are interesting and then to review what is presently known about them experimentally. Thirdly, to consider how we may predict what DAPHNE may measure. The channel of particular concern is γγ->π^0π^0. The cross-section for this process can be readly calculated in chiral perturbation theory, but the lowest order prediction is not in good agreement with existing data. However, general principles relate this process in other reactions with \π\π final states that allow a more general calculational scheme. This predicts cross-sections in much better accord with experiment. The reasons why are analyzed in detail. Moreover, we are then able to show how precision measurements of the γγ->ππ cross-section, both for π^+π^- and π^0π^0, would in turn constrain our knoledge of ππ phases.