Applicability of Perturbative Quantum Chromodynamics to High-ptExclusive Scattering

Relations among high-$p_t$ exclusive cross sections, particularly for $\gamma \gamma \to \mathrm{baryon}$-antibaryon and for meson-nucleon scattering, test the applicability of perturbative QCD in the kinematic regime of the experiments. This permits assessment of the importance of higher-order corrections and non-leading-twist contributions to the Born approximation, the extent of the "Sudakov suppression," and the validity of the asymptotic approximation to the wave functions.