Weak form factors for heavy meson decays: An update

We calculate the form factors for weak decays of B_(s) and D_(s) mesons to light pseudoscalar and vector mesons. To reveal the intimate connection between different decay modes and to be able to perform the calculations in the full physical q² region we use a relativistic dispersion approach based on the constituent quark picture. This approach gives the form factors as relativistic double spectral representations in terms of the wave functions of the initial and final mesons. The form factors have the correct analytical properties and satisfy general requirements of nonperturbative QCD in the heavy quark limit. The disadvantages of quark models related to ill-defined effective quark masses and not precisely known meson wave functions are reduced by fitting the quark model parameters to lattice QCD results for the B-->ρ transition form factors at large momentum transfers and to the measured total D-->(K,K^*)lν decay rates. This allows us to predict numerous form factors for all kinematically accessible q² values.