Leading Nucleon Form Factors in Single Gauge Boson Exchange   Approximation
  We provide a complete calculation of all leading nucleon form factors at large momentum transfer and in single gauge boson exchange approximation. In order to evaluate the required nucleon transition probability matrix elements, we combine QCD perturbation theory with an expansion in nucleon distribution amplitudes. Using leading twist nucleon distribution amplitudes only, one obtains the desired nucleon form factors. The obtained results are consistent with experimental data when we use third order polynomials for the distribution amplitudes and non-perturbative models for the coefficients. Finally, we compare our results for the Dirac form factor of the proton with previous results based on the QCD factorization theorem, where a discrepancy about the correct symmetry factor is still under discussion. We examine the calculations and propose an explanation. 
Thorsten Sachs and Patrick Sturm
hep-ph