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The local-duality formulation of QCD sum rules allows for the prediction ofhadronic form factors without knowledge of the subtle details of theirstructure. With the aid of this formalism, we take a fresh look at thebehaviours of the charged-pion elastic form factor and of the form factorsentering in the transitions of the ground-state neutral unflavouredpseudoscalar mesons pi^0, eta, eta' to one real and one virtual photon within abroad range of momentum transfers Q^2. The uncertainties induced by theapproximations inherent to this local-duality approach are estimated bystudying, in parallel to QCD, quantum-mechanical potential models, where theexact form factors, obtained by solving the Schr\"odinger equation, may becompared with the corresponding local-duality sum-rule results. For Q^2 largerthan 5-6 GeV^2, we judge the predictions of the simplest local-duality model tobe reliable and expect their accuracy to improve very fast with increasing Q^2.The large-Q^2 prediction for the pion elastic form factor should be approachedalready at moderate momentum transfer squared of approximately 4-8 GeV^2; largedeviations from its local-duality behaviour for Q^2 = 20-50 GeV^2, predicted bysome hadron-structure models, seem rather unlikely. The (eta, eta') to gamma +gamma* form factors deduced from the simplest local-duality approach exhibitexcellent agreement with experiment. In startling contrast, BaBar measurementsof the pi^0 to gamma + gamma* form factor imply local-duality violations whicheven rise with Q^2.

Local-Duality QCD Sum Rules for Pion Elastic and (pi^0, eta, eta') to gamma gamma* Transition Form Factors Revisited