Exclusive semileptonic $B$-meson decays using lattice QCD and unitarity

We present the results of the application of the Dispersion Matrix approach to exclusive semileptonic $B$-meson decays. This method allows to determine the hadronic form factors in a non-perturbative and completely model-independent way. Starting from lattice results available at large values of the momentum transfer, the behaviour of the form factors in their whole kinematical range is obtained without introducing any parameterization of their momentum dependence. We will focus on the determination of the Cabibbo-Kobayashi-Maskawa matrix elements $\mathrm{\mid }{V}_{cb}\mathrm{\mid }$ and $\mathrm{\mid }{V}_{ub}\mathrm{\mid }$ through the analysis of $B_{(s)}\to D_{(s)}^{(\ast )}\mathrm{\ell }\nu$ and $B_{(s)}\to \pi (K)\mathrm{\ell }\nu$ decays. New theoretical determinations of the Lepton Flavour Universality ratios relevant for these transitions will be also presented.