Diffractive photon production in gamma p and gamma gamma interactions - art. no. 034016.

We study the diffractive production of photons in gamma p and gamma gamma c ollisions. We specifically compute the rates for gamma*p --> gamma X and fo r gamma*y* --> gamma gamma, where X denotes the proton dissociation. We foc us on the rates at large momentum transfers, -t much greater than Lambda(2) , where we; are most confident in the use of QCD perturbation theory. Howev er, our calculations do allow us to study the -t --> 0 behavior of the gamm a*gamma* --> gamma gamma process in the region where the incoming photons a re sufficiently virtual. [S0556-2821(99)04313-1].