Study of the semileptonic decays B ->pi, D ->pi and D -> K

The semileptonic decay B ->pi is studied starting from a simple quark model that takes into into account the effect of the B*-resonance. A novel, multiply subtracted, Omnes dispersion relation has been implemented to extend the predictions of the quark model to all q(2) values accessible in the physical decay. By comparison to the experimental data, we extract | V (ub)| = (3.4 +/- 0.2(exp.)+/- 0.7(theory))10(-3). As a further test of the model, we have also studied D ->pi and D -> K decays for which we get good agreement with experiment