Probing μτ flavor-violating solutions for the muon g − 2 anomaly at Belle II

Abstract

The discrepancy between the measured value and the Standard Model prediction of the muon anomalous magnetic moment is one of the most important issues in the particle physics. It is known that introducing a mediator boson X with the μτ lepton flavor violating (LFV) couplings is one good solution to explain the discrepancy, due to the τ mass enhancement in the one-loop correction. In this paper, we study the signal of this model, i.e. the same-sign leptons, in the Belle II experiment, assuming the flavor-diagonal couplings are suppressed. We show that the Belle II experiment is highly sensitive to the scenario in the mediator mass range of O(1–10) GeV, using the e+e−→ μ±τ∓X → μ±μ±τ∓τ∓ process induced by the X .

Global analysis of leptophilic Z′ bosons

“…They can thus lead to relevant quantum corrections to leptonic precision observables and generate lepton flavour violating decays of leptons that are extremely suppressed in the SM since they vanish in the limit of massless neutrinos. The (g − 2) µ discrepancy [17,18], recently reinforced by the g − 2 experiment at Fermilab [19][20][21][22], with a tension of 4.2 σ compared to the SM prediction [23], can be explained with a Z boson heavier than the electroweak (EW) scale if it couples flavour violatingly to the second and third lepton generation [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43].…”

Ultralight scalars in leptonic observables

“…Therefore, restricting the phenomenological exploration to just pseudoscalars would miss a relatively large number of well-motivated scenarios. This has actually been the case in many recent works [29][30][31][32][33][34][35][36][37][38][39], which were mainly interested in the phenomenology of flavored axions (or ALPs) and majorons [40].…”

Probing charged lepton flavor violation with axion-like particles at Belle II

“…This particular caveat will not affect our numerical results, and so the highly suppressed X decays via g τ α couplings are not included in the numerical estimates. For m X > m τ , limits on g τ α can be derived from e − e + → l ± l ± τ ∓ τ ∓ and e − e + → l ± τ ∓ + missing [56].…”