Muonium Hyperfine Structure and the Decay ${\mu }^{+}\to e^{+}+{\bar{\nu }}_e+{\nu }_{\mu }$ in Models with Dilepton Gauge Bosons

We examine the muonium (${\mu }^{+}{e}^{-}$)-antimuonium (${\mu }^{-}{e}^{+}$) system in the models which accomodate the dilepton gauge bosons, and study their contributions to the ground state hyperfine splitting in ``muonium’'. We also consider the exotic muon decay ${\mu }^{+}\to e^{+}+{\bar{\nu }}_e+{\nu }_{\mu }$ mediated by the dilepton gauge boson, and obtain a lower bound $(M_{X^{\pm }}/g_{3l})>550 \rm GeV$ at 90% confidence level for the singly-charged dilepton mass using the unitarity relation of the Kobayashi-Maskawa matrix for the 3-family case.