The V-A sum rules and the Operator Product Expansion in complex q²-plane from tau-decay data

The operator product expansion (OPE) for the difference of vector and axial current correlators is analyzed for complex values of momentum q^2. The vector and axial spectral functions, taken from hadronic tau-decay data, are treated with the help of Borel, Gaussian and spectral moments sum rules. The range of applicability, advantages and disadvantages of each type are discussed. The general features of OPE are confirmed by the data. The vacuum expectation values of dimension 6 and 8 operators are found to be O_6=-(6.8\pm 2.1)*10^{-3} GeV^6, O_8=(7\pm 4)*10^{-3} GeV^8.