Muonium Hyperfine Structure and the Decay $ mu ^+to e^+ +overline u _e + u _{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 $mu ^+to e^+ +overline u _e + u _{mu}$ 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.