Diffractive photon production inγpandγγinteractions

We study the diffractive production of photons in gamma-p and gamma-gammacollisions. We specifically compute the rates for gamma*-p -> gamma-X and forgamma*-gamma* -> gamma-gamma, where X denotes the proton dissociation. We focuson the rates at large momentum transfers, -t >> Lambda^2, where we are mostconfident in the use of QCD perturbation theory. However, our calculations doallow us to study the -t -> 0 behaviour of the gamma*-gamma*-> gamma-gammaprocess in the region where the incoming photons are sufficiently virtual.Comment: 17 pages, 4 figure