The Light-Front Model for Exclusive Semileptonic B- and D-decays

An explicit relativistic light-front quark model is presented which gives the momentum transfer dependent form factors of weak hadronic currents among heavy pseudoscalar and vector mesons in the whole accessible kinematic region $0\leq q^2 \leq q^2_{max}$. For the numerical investigations of the $B \to D^* l \nu_l$, $B \to \rho l \nu_l$, $D\to K^* l \nu_l$ and $D \to \rho l \nu_l$ semileptonic decays the equal time wave functions corresponding to the updated version of the ISGW model are adopted. Using the available experimental information on branching fractions $BR(B \to D^* l \nu_l)$ and $BR(B \to \rho l \nu_l)$ the CKM parameters $V_{cb}$ and $V_{ub}$ were estimated: $|V_{cb}| = 0.036 \pm 0.004$, $|V_{ub}| = 0.0033 \pm 0.0004$. The model is further tested by comparison with experimental data, QCD sum rules and lattice calculations.