On the factorization of chiral logarithms in the pion form factors
  The recently proposed hard-pion chiral perturbation theory predicts that the leading chiral logarithms factorize with respect to the energy dependence in the chiral limit. This claim has been successfully tested in the pion form factors up to two loops in chiral perturbation theory. In the present paper we explain this factorization property at two loops and even show that it is valid to all orders for a subclass of diagrams. We also demonstrate that factorization is violated starting at three loops. 
Gilberto Colangelo, Massimiliano Procura, Lorena Rothen, Ramon Stucki,   Jaume Tarrus
hep-ph hep-lat nucl-th