Measurements of $BR(b \to \tau ^{-}\overline{\nu}_{\tau}X)$ and $BR(b \to \tau ^{-}\overline{\nu}_{\tau} D^{*\pm}X)$ and Upper Limits on $BR(B^{-} \to \tau^{-}\overline{\nu}_\tau)$ and $BR(b \to s\nu\overline{\nu})$

Inclusive branching ratios involving b to tau transitions are measured in approximately four million hadronic Z decays collected by the ALEPH detector at LEP. The fully-inclusive branching ratio b -> tau nu X and the semi-inclusive branching ratio b -> tau nu D*+/- X are measured to be (2.43 +/- 0.20 +/- 0.25)% and (0.88 +/- 0.31 +/- 0.28)%, in agreement with the standard model predictions. Upper limits on the branching fractions b -> tau nu and b -> s nu nubar are set to 8.3 10**-4 and 6.4 10**-4 at the 90\%~C.L. These results allow a 90\% C.L. lower limit of 0.40 (GeV/c**2)**-1 to be set on the tan(beta)/mH+/- ratio, in the framework of type-II two-Higgs-doublet models