Regular Article - Theoretical Physics
Solving the electron and muon anomalies in models
Maryland Center for Fundamental Physics, University of Maryland, 20742, College Park, MD, USA
2 Service de Physique Théorique, Université Libre de Bruxelles, Boulevard du Triomphe, CP225, 1050, Brussels, Belgium
3 School of Physics and Astronomy, University of Southampton, SO17 1BJ, Southampton, UK
Accepted: 18 November 2021
Published online: 3 December 2021
We consider simultaneous explanations of the electron and muon anomalies through a single of a extension to the Standard Model (SM). We first perform a model-independent analysis of the viable flavour-dependent couplings to leptons, which are subject to various strict experimental constraints. We show that only a narrow region of parameter space with an MeV-scale can account for the two anomalies. Following the conclusions of this analysis, we then explore the ability of different classes of models to realise these couplings, including the SM, the N-Higgs Doublet Model, and a Froggatt–Nielsen style scenario. In each case, the necessary combination of couplings cannot be obtained, owing to additional relations between the couplings to charged leptons and neutrinos induced by the gauge structure, and to the stringency of neutrino scattering bounds. Hence, we conclude that no extension can resolve both anomalies unless other new fields are also introduced. While most of our study assumes the Caesium measurement, our findings in fact also hold in the case of the Rubidium measurement, despite the tension between the two.
© The Author(s) 2021
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