Inclusive $B_c$ Decays As A QCD Lab

Phenomenological models of heavy flavour decays differ significantly in their predictions of global features of $B_c$ decays, like the $B_c$ lifetime or the relative weight of $c\ra s$ and $b\ra c$ transitions. The $1/m_Q$ expansion which is directly based on QCD allows predictions on the pattern to be expected, namely $\tau (B_c)$ to lie well below 1 psec with $c\ra s$ dominating over $b\ra c$ and a reduced semileptonic branching ratio. Due to interference effects one also predicts a lower charm content in the final states of $B_c$ decays than naively anticipated. The numerical aspect of the predictions, however, has to be viewed with considerable caution since one cannot expect the $1/m_c$ expansion to converge readily for $\Delta C=1$ transitions.