Semileptonic decays ofBandDmesons in the light-front formalism

The light-front formalism is used to present a relativistic calculation of form factors for semileptonic $D$ and $B$ decays in the constituent quark model. The quark-antiquark wave functions of the mesons can be obtained, in principle, from an analysis of the meson spectrum, but are approximated in this work by harmonic-oscillator wave functions. The predictions of the model are consistent with the experimental data for $B$ decays. The Kobayashi-Maskawa (KM) matrix element $\left|V_{\mathrm{cs}}\right|$ is determined by a comparison of the experimental and theoretical rates for $D^0\to K^{-}{e}^{+}\nu$ and is consistent with a unitary KM matrix for three families. The predictions for $D\to K^{*}$ transitions are in conflict with the data.