Diffractive photon production inγpandγγinteractions

We study the diffractive production of photons in $\gamma p$ and $\gamma \gamma$ collisions. We specifically compute the rates for ${\gamma }^{*}\overrightarrow{p}\gamma X$ and for ${\gamma }^{*}{\gamma }^{*}\to \gamma \gamma ,$ where X denotes the proton dissociation. We focus on the rates at large momentum transfers, $-t\gg {\Lambda }^2,$ where we are most confident in the use of QCD perturbation theory. However, our calculations do allow us to study the $-\overrightarrow{t}0$ behavior of the ${\gamma }^{*}{\gamma }^{*}\to \gamma \gamma$ process in the region where the incoming photons are sufficiently virtual.