Decay constants, semi-leptonic and non-leptonic decays in a Bethe-Salpeter Model

We evaluate the decay constants for the B and $D$ mesons and the form factors for the semileptonic decays of the B meson to $D$ and $D^{\ast }$ mesons in a Bethe-Salpeter model. From data we extract $V_{cb}=0.039\pm 0.002$ from ${\bar B} \to D^* l {\bar{\nu}} $and$V_{cb}=0.037 \pm 0.004$from${\bar B} \to D l {\bar{\nu}} $ decays. The form factors are then used to obtain non-leptonic decay partial widths for $B\to D\pi (K)$ and $B\to DD(D_s)$ in the factorization approximation.