6533b86dfe1ef96bd12c941a

RESEARCH PRODUCT

Determination of the chiral couplingsL10andC87from semileptonicτdecays

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Using recent precise hadronic {tau}-decay data on the V-A spectral function, and general properties of QCD such as analyticity, the operator product expansion, and chiral perturbation theory, we get accurate values for the QCD chiral order parameters L{sub 10}{sup r}(M{sub {rho}}) and C{sub 87}{sup r}(M{sub {rho}}). These two low-energy constants appear at order p{sup 4} and p{sup 6}, respectively, in the chiral perturbation theory expansion of the V-A correlator. At order p{sup 4} we obtain L{sub 10}{sup r}(M{sub {rho}})=-(5.22{+-}0.06)x10{sup -3}. Including in the analysis the two-loop (order p{sup 6}) contributions, we get L{sub 10}{sup r}(M{sub {rho}})=-(4.06{+-}0.39)x10{sup -3} and C{sub 87}{sup r}(M{sub {rho}})=(4.89{+-}0.19)x10{sup -3} GeV{sup -2}. In the SU(2) chiral effective theory, the corresponding low-energy coupling takes the value l{sub 5}=13.30{+-}0.11 at order p{sup 4}, and l{sub 5}=12.24{+-}0.21 at order p{sup 6}.