Vincenzo Cirigliano, Jordy de Vries, Leendert Hayen, Emanuele Mereghetti, and André Walker-Loud, Pion-Induced Radiative Corrections to Neutron β Decay, Phys. Rev. Lett. 129, 121801, 2022

We compute the electromagnetic corrections to neutron β decay using a low-energy hadronic effective field theory. We identify new radiative corrections arising from virtual pions that were missed in previous studies. The largest correction is a percent-level shift in the axial charge of the nucleon proportional to the electromagnetic part of the pion-mass splitting. Smaller corrections, comparable to anticipated experimental precision, impact the β−ν angular correlations and the β asymmetry. We comment on implications of our results for the comparison of the experimentally measured nucleon axial charge with first-principles computations using lattice QCD and on the potential of β decay experiments to constrain beyond-the-standard-model interactions.

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