Low's soft photon corrections to dipion tau decays and their impact on aμ

The O(α) real-photon corrections to τ−→π−π0ντ calculations of the corresponding radiative amplitude up to O(k0) (k, the photon momentum), contribute to radiative corrections with almost identical numerical results for the di-pion invariant-mass spectrum. The pion form factor required to compute the corrections includes three isovector resonances, which allows to extend the range of validity of radiative corrections in the whole range of momentum transfer accessible to tau lepton decays. An estimate of the corresponding isospin breaking correction to be applied to τ decay data used to predict the leading hadronic contribution to the muon anomalous magnetic moment is provided.