Pion parameters and four quark condensates from τ-decay data

A modified finite energy sum rules procedure is presented and applied for the phenomenological analysis of the difference of vector and axial-vector two-point current correlators. In the chiral limit π→evy decay axial formfactorF A , electro-magnetic difference of pion masses and the four quark condensates of dimensions six and eight are determined with improved accuracy, using the data on τ→v+nπ decays obtained by ARGUS collaboration. Our values forF A and Δmem are close to the measured ones, whileC6 exceeds 2.5–3 times the value given by the vaccum saturation hypothesis.