We search for neutral heavy leptons that are isosinglets under the standard SU (2)l gauge group. Such neutral heavy leptons are expected in many extensions of the standard model. Three types of heavy leptons Ne, N^, NT associated with the three neutrino types v* have been directly searched for and no evidence for a signal has been found. We set the limit Br(Z° -► z//N*) < 3 x 10" 5 at the 95% CL for the mass range from 3 GeV up to m%.

The results of the searches for neutral Higgs boson production in the process e+e---+ Z* Ho are reported, focusing on Higgs boson masses below 70 GeV. The data sample consists of three million hadronic Z" decays collected by the L3 experiment at LEP from 1991 through 1994. No signal is found leading to a lower limit on the mass of the Standard Model Higgs boson of 60.2 GeV at 95% C.L.These results are also interpreted in the framework of the General Two Doublet Model and limits on the nonstandard Higgs boson production through the process e + -e 4 Z* ho are set. A lower limit of 66.7 GeV at 95% CL. is obtained for the case where the Higgs decays into an invisible final state.

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A search for exclusive decays of Bt and Bf mesons has been performed in the channels Bi 4 Jq, Bz + Jq Bi 4 Jr0 and Bg -_) J.R'. The data sample consisted of more than three and half million hadronic Z decays collected by the L3 experiment at LEP from 1991 through 1995. No candidate events have been observed for any of the modes thus determining upper limits at 90% confidence level: 3.2 x low4 on Br(Bj --+ Jr') and the first experimental limits: Br(J3: -+ Jv) < 1.2 x 10w3, Br(Bt -+ 57) < 3.8 x 10p3, Br(By -+ Jr') < 1.2 X 10U3.

Using a data sample of 1475 000 Z-f q4(y) events collected during 1994 with the L3 detector at LEP, we have studied the purely leptonic decays of heavy flavour mesons, D;