Large-angle two-photon exclusive channels in quantum chromodynamics

Detailed leading-order quantum-chromodynamics (QCD) predictions are given for the scaling, angular, and helicity dependence of the reactions ..gamma gamma -->..MM-bar (M = ..pi.., K, 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 phi/sub M/(x,Q). Other related two-photon channels such as ..gamma gamma --> gamma..rho, ..gamma..*..gamma --> pi../sup 0/,eta/sup 0/,..nu..', and eta/sub c/..--> gamma gamma.. are also discussed. We also prove the existence of a fixed Regge singularity at J = 0 which couples to ..gamma..rho..--> gamma..rho in the t channel but not to ..gamma pi --> gamma pi...