Radiative corrections to neutron β decay with explicit Δ(1232) degrees of freedom
Abstract
We study electromagnetic radiative corrections to neutron β decay within chiral perturbation theory extended to include the Δ(1232) resonance as an explicit degree of freedom. Building on a previous analysis performed in the Δ-less theory, we identify and compute additional loop contributions with intermediate Δ states at leading and next-to-leading order in the small-scale expansion, and match the results to the pionless effective field theory. We find that the convergence of the chiral expansion significantly improved in the Δ-full calculation. The electromagnetic shift in the axial coupling is reduced by 25% compared to the Δ-less result. The correction remains at the percent level and is phenomenologically significant for the comparison between experimental extractions and lattice-QCD determinations of the nucleon axial charge. We also obtain a new Δ-induced contribution to the weak magnetism term, which is an order of magnitude smaller than the pion-loop result and negligible for upcoming experiments.
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BibTeX
@misc{gialidi2026radiative,
title = {{Radiative corrections to neutron $β$ decay with explicit $Δ(1232)$ degrees of freedom}},
author = {Lemonia Gialidi and Emanuele Mereghetti and Jordy de Vries},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2608.14794},
eprint = {2608.14794},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.14794},
}
RIS
TY - UNPB
TI - Radiative corrections to neutron β decay with explicit Δ(1232) degrees of freedom
AU - Lemonia Gialidi
AU - Emanuele Mereghetti
AU - Jordy de Vries
PY - 2026
DA - 2026/09/23
PB - arXiv
DO - 10.48550/arxiv.2608.14794
UR - https://arxiv.org/abs/2608.14794
AB - We study electromagnetic radiative corrections to neutron β decay within chiral perturbation theory extended to include the Δ(1232) resonance as an explicit degree of freedom. Building on a previous analysis performed in the Δ-less theory, we identify and compute additional loop contributions with intermediate Δ states at leading and next-to-leading order in the small-scale expansion, and match the results to the pionless effective field theory. We find that the convergence of the chiral expansion significantly improved in the Δ-full calculation. The electromagnetic shift in the axial coupling is reduced by 25% compared to the Δ-less result. The correction remains at the percent level and is phenomenologically significant for the comparison between experimental extractions and lattice-QCD determinations of the nucleon axial charge. We also obtain a new Δ-induced contribution to the weak magnetism term, which is an order of magnitude smaller than the pion-loop result and negligible for upcoming experiments.
ER -