EVOLUTION OF THE PION DISTRIBUTION AMPLITUDE IN NEXT-TO-LEADING ORDER

The evolution of the pion distribution amplitude in next-to-leading order is studied for a fixed and a running coupling constant. In both cases, the evolution provides a logarithmic modification in the end point region. Assuming a simple parametrization of the distribution amplitude at a scale of Q00.5 GeV, it is shown numerically that these effects are large enough at Q2 GeV that they have to be taken into account in the next-to-leading-order analysis for exclusive processes. Alternatively, by introducing a new distribution amplitude that evolves more smoothly, this logarithmic modification can be included in the hard-scattering part of the considered process. © 1995 The American Physical Society.