Lava flowing over pQCD: gamma* gamma -> pi^0
Anatoly Radyushkin
JLab/ODU
A scenario is investigated in which the leading-twist pion distribution
amplitude phi_pi (x) is approximated by the pion decay constant f_pi
for all essential values of the light-cone fraction x.
A model for the light-front wave function Psi(x,k_perp) is proposed that
produces such a distribution amplitude and has a rapidly decreasing
(exponential for definiteness) dependence on the light-front energy
combination k_perp^2/x(1-x).
It is shown that this model easily reproduces the fit of recent
large-Q^2 BaBar data on the photon-pion transition form factor. Some
aspects of scenario with flat pion distribution amplitude are discussed.