Isospin-breaking corrections to light-meson leptonic decays from lattice simulations at physical quark masses

Peter Boyle, Matteo Di Carlo, Felix Erben, Vera Gülpers, Maxwell T. Hansen, Tim Harris, Nils Hermansson-Truedsson, Raoul Hodgson, Andreas Jüttner, Fionn hÓgáin, Antonin Portelli, James Richings, Andrew Zhen Ning Yong

    Research output: Contribution to journalArticlepeer-review


    The decreasing uncertainties in theoretical predictions and experimental measurements of several hadronic observables related to weak processes, which in many cases are now smaller than O(1%), require theoretical calculations to include subleading corrections that were neglected so far. Precise determinations of leptonic and semi-leptonic decay rates, including QED and strong isospin-breaking effects, can play a central role in solving the current tensions in the first-row unitarity of the CKM matrix. In this work we present the first RBC/UKQCD lattice calculation of the isospin-breaking corrections to the ratio of leptonic decay rates of kaons and pions into muons and neutrinos. The calculation is performed at fixed lattice spacing (a−1 ≃ 1.730 GeV) on a 483× 96 volume with Nf = 2 + 1 dynamical quarks close to the physical point and domain wall fermions in the Möbius formulation are employed. Long-distance QED interactions are included according to the QEDL prescription and the crucial role of finite-volume electromagnetic corrections in the determination of leptonic decay rates, which produce a large systematic uncertainty, is extensively discussed. Finally, we study the different sources of uncertainty on |Vus|/|Vud| and observe that, if finite-volume systematics can be reduced, the error from isospin-breaking corrections is potentially sub-dominant in the final precision of the ratio of the CKM matrix elements.

    Original languageEnglish
    Article number242
    JournalJournal of High Energy Physics
    Issue number2
    Publication statusPublished - 2023 Mar

    Subject classification (UKÄ)

    • Subatomic Physics

    Free keywords

    • CKM Parameters
    • Hadronic Matrix Elements and Weak Decays
    • Lattice QCD
    • Standard Model Parameters


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