Muon decay across scales: from LEFT to SMEFT
Abstract
We revisit precision muon decay in the framework of the LEFT by considering how the LEFT perturbs the total rate as well as the standard and polarization-dependent Michel parameters. We derive the dependence of these observables on the dimension-five and -six LEFT operators, including lepton number violating operators, allowing for arbitrary neutrino flavor assignments. We consider fits of the LEFT to the muon decay data, in particular an approach to neutrino flavor general fits that does not respect the LEFT power counting and assuming new physics couples to all flavors equally and therefore allows for a consistent fit. We then consider how new physics imprints on the SMEFT and subsequently the LEFT in order to constrain specific scenarios of single-field extensions as well as two motivated two-field extensions. While we infer associated mass scales for these scenarios in the hundreds of GeV to multi-TeV range we also find that for the specific cases of lepton number violation, neutrino mass constraints from operator mixing are more restrictive than muon decay.
Related
- An Operator Analysis of Radiative Muon Decay
- Suitability studies of exotic muon decay at the High Intensity heavy-ion Accelerator Facility
- Implications of the muon anomalous magnetic moment in a doublet left-right symmetric model
- PDF effects in high-mass Drell-Yan SMEFT analyses across flavour space
- Radiative Higgs decay to ψ(4230)
BibTeX
@misc{moritz2026muon,
title = {{Muon decay across scales: from LEFT to SMEFT}},
author = {Carl Jakob Moritz and Tyler Corbett},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.12051},
eprint = {2609.12051},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.12051},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Muon decay across scales: from LEFT to SMEFT
AU - Carl Jakob Moritz
AU - Tyler Corbett
PY - 2026
DA - 2026/09/23
PB - arXiv
DO - 10.48550/arxiv.2609.12051
UR - https://arxiv.org/abs/2609.12051
AB - We revisit precision muon decay in the framework of the LEFT by considering how the LEFT perturbs the total rate as well as the standard and polarization-dependent Michel parameters. We derive the dependence of these observables on the dimension-five and -six LEFT operators, including lepton number violating operators, allowing for arbitrary neutrino flavor assignments. We consider fits of the LEFT to the muon decay data, in particular an approach to neutrino flavor general fits that does not respect the LEFT power counting and assuming new physics couples to all flavors equally and therefore allows for a consistent fit. We then consider how new physics imprints on the SMEFT and subsequently the LEFT in order to constrain specific scenarios of single-field extensions as well as two motivated two-field extensions. While we infer associated mass scales for these scenarios in the hundreds of GeV to multi-TeV range we also find that for the specific cases of lepton number violation, neutrino mass constraints from operator mixing are more restrictive than muon decay.
ER -