Pion Helicity Structure And Its Consequence For The Hard Scattering Form   Factor
  In a study of the elastic pion form factor for large momentum transfers based on a modified perturbative QCD (PQCD) approach we have included helicity components that are customarily neglected. Along with the inclusion of transverse momentum, this gives a large suppression of the form factor from the prediction of the original hard scattering model based on PQCD in the $Q^{2}$ domain where experimental data are available. We conclude that nonperturbative contributions will dominate in this region. 
Siwen Wang (University of Maryland, Collge Park, MD USA) and Leonard   S. Kisslinger (Carnegie Mellon University, Pittsburgh...