Polarized \Lambda_b \to X_c \tau \nu in the SM and THDM

The inclusive rate and $\tau$ spectrum for a polarized ${\mathrm{\Lambda }}_b$ -baryon to decay to charm hadronic final states and leptons $\tau \nu$ in the SM and a two-Higgs doublet model are computed.The $O({\alpha }_s)$ QCD corrections to $\tau$ spectrum in the two-Higgs model are also given.