Published: 2001
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The authors investigate a model QCD sum rule for the pion wave function[var-phi][sub[pi]](x) based on the non-diagonal correlator whose perturbative spectral density vanishes and[Phi](x, M[sup 2]), the theoretical side of the sum rule, consists of condensate contributions only. They study the dependence of[Phi](x, M[sup 2]) on the Borel parameter M[sup 2] and observe that[Phi](x, M[sup 2]) has a humpy form, with the humps becoming more and more pronounced when M[sup 2] increases. They demonstrate that this phenomenon reflects just the oscillatory nature of the higher states wave functions, while the lowest state wave function, [var-phi][sub[pi]](x), extracted from their QCD sum rule analysis, has no humps, is rather narrow and its shape is close to the asymptotic form[var-phi][sub[pi]][sup as](x)= 6x(1[minus]x).