Lattice and perturbative QCD analysis of exclusive processes

Abstract

We use the results of a Monte Carlo simulation of quantum chromodynamics in the quenched approximation to compute the first two moments of the \ensuremath{\pi} and \ensuremath{\rho} distribution amplitude. Our results turn out to be surprisingly large, and we discuss some of the phenomenological implications of this turn of events. In addition to the distribution amplitude itself, we predict the pion form factor and the cross section for \ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}${\ensuremath{\pi}}^{0}$${\ensuremath{\pi}}^{0}$, and we compare the former with experiment. We also contrast lattice-gauge-theory predictions with those of QCD sum rules.