Quark mass difference effects in hadronic Fermi matrix elements from first principles

It was recently estimated that the strong isospin-symmetry breaking (ISB) corrections to the Fermi matrix element in free neutron decay could be of the order 10-4, one order of magnitude larger than the naive estimate based on the Behrends-Sirlin-Ademollo-Gatto theorem. To investigate this claim, we derive a general expression of the leading ISB correction to hadronic Fermi matrix elements, which takes the form of a four-point correlation function in lattice gauge theory and is straightforward to compute from first principles. Our formalism paves the way for the first determination of such correction in the neutron sector with fully-controlled theory uncertainties.(c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons .org /licenses /by /4 .0/). Funded by SCOAP3.

Automated summary

Recent estimates suggest that the strong isospin-symmetry breaking (ISB) corrections to the Fermi matrix element in free neutron decay may be one order of magnitude larger than the naive estimate based on a theorem. To investigate this claim, we derive a general expression for the leading ISB correction to hadronic Fermi matrix elements, which can be computed from first principles. Our formalism opens up the possibility of determining this correction in the neutron sector with fully-controlled theory uncertainties.