Pion wave function from QCD sum rules with nonlocal condensates

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).