Probing Neutrinophilic Scalars in Muon Decays
Abstract
The non-standard self-interactions of neutrinos could be induced by (light) scalars that couple primarily to neutrinos. In this work, we investigate the effects of neutrinophilic scalars ϕ on muon decays at the tree, 1-loop and 2-loop levels, considering both Dirac and Majorana neutrinos. The most phenomenologically interesting processes are the 1-loop decay μ→ e ϕϕ and ϕ-induced decay μ→ e γ at the 2-loop order from the same coupling geff, and the 1-loop corrections of ϕ to the SM muon decay and the four-body muon decays μ- → e- νμνμϕ, e- ν̅e ν̅e ϕ, both induced by the coupling heμ of ϕ to Majorana neutrinos. The current experimental bounds on μ→ e γ provide the most stringent limits on the coupling geff, up to roughly 0.064, for the scalar mass mϕ≳ 8.7 MeV. The precise GF measurements constrain the coupling |heμ| down to roughly $0.027$, with the scalar mass mϕ constrained up to roughly $5.9$ TeV. For mϕ≳ cal O(GeV), the GF measurements are more stringent than other existing laboratory, astrophysical and cosmological constraints. Some other ϕ-induced processes are also possible, which are, however, heavily suppressed by the tiny neutrino masses and/or the loop factor.
Related
- Precision Electroweak Constraints on Neutrinophilic Scalars
- Missing Mass Matters: Neutrinophilic Scalar in D-Meson Decays
- Probing Neutrinophilic Axion-Like Particles in Tritium Beta Decay
- Production of lepton-flavor-violating scalars through resonant positive-muon annihilation on atomic electrons
- Probing pair production of long-lived scalars via an off-shell Standard-Model-like Higgs boson at the LHC
BibTeX
@misc{zhang2026probing,
title = {{Probing Neutrinophilic Scalars in Muon Decays}},
author = {Yongchao Zhang and Zhong Zhang},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2609.13964},
eprint = {2609.13964},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.13964},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Probing Neutrinophilic Scalars in Muon Decays
AU - Yongchao Zhang
AU - Zhong Zhang
PY - 2026
DA - 2026/10/02
PB - arXiv
DO - 10.48550/arxiv.2609.13964
UR - https://arxiv.org/abs/2609.13964
AB - The non-standard self-interactions of neutrinos could be induced by (light) scalars that couple primarily to neutrinos. In this work, we investigate the effects of neutrinophilic scalars ϕ on muon decays at the tree, 1-loop and 2-loop levels, considering both Dirac and Majorana neutrinos. The most phenomenologically interesting processes are the 1-loop decay μ→ e ϕϕ and ϕ-induced decay μ→ e γ at the 2-loop order from the same coupling g_eff, and the 1-loop corrections of ϕ to the SM muon decay and the four-body muon decays μ^- → e^- ν_μν_μϕ, e^- ν̅_e ν̅_e ϕ, both induced by the coupling h_eμ of ϕ to Majorana neutrinos. The current experimental bounds on μ→ e γ provide the most stringent limits on the coupling g_eff, up to roughly 0.064, for the scalar mass m_ϕ≳ 8.7 MeV. The precise G_F measurements constrain the coupling |h_eμ| down to roughly $0.027$, with the scalar mass m_ϕ constrained up to roughly $5.9$ TeV. For m_ϕ≳ cal O(GeV), the G_F measurements are more stringent than other existing laboratory, astrophysical and cosmological constraints. Some other ϕ-induced processes are also possible, which are, however, heavily suppressed by the tiny neutrino masses and/or the loop factor.
ER -