A note on isospin violation in Pl2(gamma) decays
Abstract
We discuss the size of isospin violating effects of both electromagnetic (e ≠ 0) and strong (mu ≠ md) origin in P 2 (γ) decays. Our results are relevant for the extraction of |Vus/Vud| from the measured ratio of the Kμ 2 (γ) and πμ 2 (γ) decay widths combined with FK/Fπ obtained in lattice calculations in the isospin limit. We point out that strong isospin-breaking corrections, neglected in previous studies, enter at the same level as the electromagnetic effects. The updated value for the ratio of CKM elements reads |Vus/Vud| = 0.2316(12).
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