The reliability of pQCD approach in pion electromagnetic form factor
  The pion electromagnetic form factor with leading and next-to-leading twist corrections are studied in the framework of pQCD approach. We find that, at small momentum transfer regions, Sudakov effects cannot provide a strong enough suppression of the non-perturbative contributions coming from large transverse separations, but at large momentum transfer region, non-perturbative contributions can be effectively suppressed. So pQCD approach can be applied at large momentum transfer region. At the energy region where experiment can access so far, i.e. Q < 4GeV, pQCD prediction can not be precise because there may be a quite large part of contributions coming from non-perturbative region. The calculation of power corrections may not be performed systematically in pQCD framework. 
Zheng-Tao Wei, Mao-Zhi Yang