Improved limits on lepton-flavor-violating decays of light pseudoscalars via spin-dependent $\mu \to e$ conversion in nuclei

Abstract

Lepton-flavor-violating decays of light pseudoscalars, $P={\pi }^0,\eta ,{\eta }^{\prime }\to \mu e$, are stringently suppressed in the Standard Model up to tiny contributions from neutrino oscillations, so that their observation would be a clear indication for physics beyond the Standard Model. However, in effective field theory such decays proceed via axial-vector, pseudoscalar, or gluonic operators, which are, at the same time, probed in spin-dependent $\mu \to e$ conversion in nuclei. We derive master formulae that connect both processes in a model-independent way in terms of Wilson coefficients, and study the implications of current $\mu \to e$ limits in titanium for the $P\to \mu e$ decays. We find that these indirect limits surpass direct ones by many orders of magnitude.

9 pages, 2 figures; journal version

References in corpus (15)

• FLAG Review 2021
• Technical design of the phase I Mu3e experiment
• Improved limits for Higgs-portal dark matter from LHC searches
• Extracting the sigma-term from low-energy pion-nucleon scattering
• Dispersive analysis of the scalar form factor of the nucleon
• Improved predictions for $\mu \to e$ conversion in nuclei and Higgs-induced lepton flavor violation
• Search for Lepton Flavor Violating Decays of the Neutral Kaon
• Masses and decay constants of the $\eta$ and ${\eta }^{\prime }$ mesons from lattice QCD
• Lepton flavor violating quarkonium decays
• The pion-nucleon sigma term from lattice QCD
• Contribution of the QCD $\Theta$-term to nucleon electric dipole moment
• Completeness and Complementarity for $\mu \to e\gamma$, $\mu \to 3e$ and $\mu \to e$ conversion
• Search for lepton number and flavour violation in $K^{+}$ and ${\pi }^0$ decays
• Reach and complementarity of $\mu \to e$ searches
• Next-to-leading order scalar contributions to $\mu \to e$ conversion

Cited by in corpus (11)

• On the role of isospin violation in the pion-nucleon $\sigma$-term
• Nuclear-level Effective Theory of $\mu \to e$ Conversion: Formalism and Applications
• Effective theory tower for $\mu \to e$ conversion
• Nuclear-Level Effective Theory of $\mu \to e$ Conversion
• Improved evaluation of the electroweak contribution to muon $g-2$
• Uncertainty quantification for $\mu \to e$ conversion in nuclei: charge distributions
• Ab initio calculations of overlap integrals for $\mu \to e$ conversion in nuclei
• Nonrelativistic nuclear reduction for tensor couplings in dark matter direct detection and $\mu \to e$ conversion
• A New Determination of the (Z,A) Dependence of Coherent Muon-to-Electron Conversion
• Nucleon mass: trace anomaly and $\sigma$-terms
• Constraining lepton flavor violating SMEFT $2q2\ell$ operators from low-energy cLFV processes