Year: 2026
Type: preprint
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 $μ\to e ϕϕ$ and $ϕ$-induced decay $μ\to e γ$ at the 2-loop order from the same coupling $g_{\rm eff}$, and the 1-loop corrections of $ϕ$ to the SM muon decay and the four-body muon decays $μ^- \to e^- ν_μν_μϕ,\, e^- \barν_e \barν_e ϕ$, both induced by the coupling $h_{eμ}$ of $ϕ$ to Majorana neutrinos. The current experimental bounds on $μ\to e γ$ provide the most stringent limits on the coupling $g_{\rm eff}$, up to roughly 0.064, for the scalar mass $m_ϕ\gtrsim 8.7$ 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 $m_ϕ\gtrsim {\cal O}({\rm GeV})$, 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.
Source: arXiv (Cornell University)
Authors: Zhang, Yongchao, Zhang, Zhong
Institutions: Peking University, Southeast University
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7213328058