Probing $\mu\tau$ flavor-violating solutions for the muon $g-2$ anomaly at Belle II

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 $\mu \tau$ lepton flavor violating (LFV) couplings is one good solution to explain the discrepancy, due to the $\tau$ 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 ${\cal O}(1-10)$~GeV, using the $e^+e^- \to \mu^\pm\tau^\mp X \to\mu^\pm \mu^\pm \tau^\mp \tau^\mp$ process induced by the $X$.