Pseudoscalar-Meson Form Factors: A Fresh Look by QCD Sum Rules
  Confronted with some surprising claims about experimentally measured or theoretically expected dependencies on the involved momentum transfer of various form factors of pseudoscalar mesons, we reassess the present status of these quantities by means of QCD sum rules. This approach provides well-developed and very efficient tools to relate in an analytical manner the parameters of QCD to the empirical properties of hadrons. Within this framework, we show that a few theoretical findings for the pion elastic form factor and one experimental result for the pion-to-photon transition form factor are at odds with rather general fundamental considerations. 
Irina Balakireva, Wolfgang Lucha, Dmitri Melikhov
hep-ph hep-ex nucl-th