From Hadronic τ Decays to the Chiral Couplings and ⁎

A sum rule analysis of the hadronic τ-decay data can be used to determine the low-energy constants and . These constants are QCD chiral-order parameters, which appear at order p4 and p6, respectively, in the chiral perturbation theory expansion of the V−A correlator. At order p4 we obtain . Including in the analysis the order p6 contributions, we get and .