MUONIUM HYPERFINE-STRUCTURE AND THE DECAY MU(+)-]E(+)+(NU)OVER-BAR(E)+NU(MU)

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+ --> e + +nu(e)BAR +nu(mu) mediated by the dilepton gauge boson, and obtain a lower bound (M(X) +/-/g3l) > 550 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.