Muonium hyperfine structure and the decay ${\mu }^{+}\to e^{+}+{\overline{\nu }}_e+{\nu }_{\mu }$ in models with dilepton gauge bosons

We examine the muonium (${\mu }^{-}{e}^{+}$)-antimuonium (${\mu }^{-}{e}^{+}$) system in the models which accommodate the dilepton gauge bosons, and study their contributions to the ground state hyperfine splitting in "muonium." We also consider the exotic muon decay ${\mu }^{+}\to e^{+}+{\overline{\nu }}_e+{\nu }_{\mu }$ mediated by the dilepton gauge boson, and obtain a lower bound $\frac{M_{X^{\pm }}}{g_{3i}}$ GeV at a 90% confidence level for the singly-charged dilepton mass using the unitarity relation of the Kobayashi-Maskawa matrix for the three-family case.