Tau Polarization in ${\mathrm{\Lambda }}_b\to X_c\tau \bar{\nu }$ and $B\to X_c\tau \bar{\nu }$

We discuss the longitudinal and transverse $\tau$-polarization in inclusive decays of hadrons containing $b$-quarks. The calculation is performed by means of an OPE in HQET. Some mathematical difficulties in calculating transverse polarizations are explained. Numerical results are presented for longitudinal and for transverse polarizations, both in and perpendicular to the decay plane.