Abstract
Detailed leading-order quantum-chromodynamics (QCD) predictions are given for the scaling, angular, and helicity dependence of the reactions $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}M\overline{M}$ ($M=\ensuremath{\pi},K,\ensuremath{\rho}$, etc.) at large momentum transfer. In addition to providing a basic test of QCD at short distances, measurements can be used to determine the process-independent meson distribution amplitudes ${\ensuremath{\varphi}}_{M}(x,Q)$. Other related two-photon channels such as $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\rho}$, ${\ensuremath{\gamma}}^{*}\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0},{\ensuremath{\eta}}^{0},{\ensuremath{\eta}}^{\ensuremath{'}}$, and ${\ensuremath{\eta}}_{c}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$ are also discussed. We also prove the existence of a fixed Regge singularity at $J=0$ which couples to $\ensuremath{\gamma}\ensuremath{\rho}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\rho}$ in the $t$ channel but not to $\ensuremath{\gamma}\ensuremath{\pi}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\pi}$.
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