Abstract
Recently, it was pointed out that the electron and muon g − 2 discrepancies can be explained simultaneously by a single flavor-violating axion-like particle (ALP). We show that the parameter regions favored by the muon g − 2 are already excluded by the muonium-antimuonium oscillation bound. In contrast, those for the electron g − 2 can be consistent with this bound when the ALP is heavier than 1.5 GeV. We propose to search for a signature of the same-sign and same-flavor lepton pairs and the forward-backward muon asymmetry to test the model at the Belle II experiment.
Highlights
Compared to the previous result based on the measurement of the rubidium mass [21]
We show that the parameter regions favored by the muon g − 2 are already excluded by the muonium-antimuonium oscillation bound
We propose to search for a signature of the same-sign and same-flavor lepton pairs and the forward-backward muon asymmetry to test the model at the Belle II experiment
Summary
Let us introduce ALP (a), which is a real (pseudo-) scalar field, with flavor-violating interactions. For the flavor-conserving interaction (i = j), it is noticed that contributions of vii vanish automatically and only the pseudo-scalar term is left This is obvious if we consider a case when the ALP couples to on-shell fermions. The first condition is required because other types of LFV decays such as τ → μγ, τ → eγ, τ → μμe, and τ → μee can be generated by combining veμ, aeμ with those including the tau lepton [34, 44] Such a hierarchy between the ALP interactions could be obtained from Z4 lepton flavor symmetry The ALP couplings are required to satisfy Im (yV )eμ(yA)∗eμ < 10−6 [| (yA)eμ |2 −| (yV )eμ |2]
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