Prof. Dmitri Melikhov (HEPHY Vienna Austria & SINP Moscow Russia)
We calculate the pion form factor making use of a local-duality (LD) version of QCD sum rules. To probe the accuracy of the obtained predictions we consider in parallel to QCD a potential model with an interaction consisting of Coulomb and confining parts. In this case, the exact form factor may be obtained from the solution of the Schrödinger equation and confronted with the result from the quantum-mechanical LD sum rule. We employ parameters of the potential model appropriate for hadron physics and show that, independently of the details of the confining interaction, the maximal deviation of the LD form factor from the exact form factor is observed in the region Q²=4-8 GeV². At higher Q, the accuracy of the LD sum rule increases rather fast with Q. In QCD, no disagreement between the LD sum rule for the pion form factor and experimental data at Q²=1-6 GeV² has been observed until now. We argue that this feature leads to important consequences for the pion form factor at larger momentum transfers, up to the asymptotically large values.