Violation of Quark-Hadron Duality and Spectral Chiral Moments in QCD

We analyze the spectral moments of the V-A two-point correlation function. Using all known short-distance constraints and the most recent experimental data from tau decays, we determine the lowest spectral moments, trying to assess the uncertainties associated with the so-called violations of quark-hadron duality. We have generated a large number of “acceptable” spectral functions, satisfying all conditions, and have used them to extract the wanted hadronic parameters through a careful statistical analysis. We obtain accurate values for the χPT couplings L10 and C87, and a realistic determination of the dimension six and eight contributions in the operator product expansion, O6 = ( −5.4 − 1.6 ) ·10−3 GeV and O8 = ( −8.9 − 7.4 ) ·10−3 GeV, showing that the duality-violation effects have been underestimated in previous literature.