This dissertation measures an inclusive branching fraction of (13.9 +- 2.0/sub -2.4//sup +2.1/)% for the decay tau− .-->. nu/sub tau/.pi.−.pi.° + nh° where h° is a .pi.° or an eta and n greater than or equal to 1. The data sample, obtained with the TPC detector facility at PEP, corresponds to an integrated luminosity of 72 pb−1 at 29 GeV center of mass energy. The measured value for this branching fraction is somewhat greater than the theoretical prediction and, taking errors into account, resolves the present difference between the inclusive and the sum of the exclusive tau− branching fractions into one charged prong. In addition, a lower limit of 8.3% (95% CL) is placed on the branching fraction B(tau− .-->. nu/sub tau/.pi.−.pi.°.pi.°).

The authors report on analyses of tau lepton decays?− →?K−?{sub?} and?− →??−?{sub?}, with? →??−?°, using 470 fb−1 of data from the BABAR experiment at PEP-II, collected at center-of-mass energies at and near the?(4S) resonance. They measure the branching fraction for the?− →?K−?{sub?} decay mode,?({tau}− →?K−?{sub {tau}}) = (1.42 ± 0.11(stat) ± 0.07(syst)) x 10−4, and report a 95% confidence level upper limit for the second-class current process {tau}− →??−?{sub {tau}},?({tau}− →??−?{sub {tau}})