Ward identities, B → V transition form factors and applications

Long distance effects are studied in the rare exclusive semileptonic B(d,s) → Vℓ⁺ℓ⁻ decays, where V denotes a K* or ϕ meson. The form factors, which describe the meson transition amplitudes in the effective Hamiltonian approach, are calculated by means of Ward identities, experimental constraints and extrapolated within a general vector meson dominance framework. These form factors are then compared to the ones obtained in Lattice QCD simulations, with Light Cone Sum Rules and a Dyson-Schwinger equation approach. Additionally, the B_d → K*ℓ⁺ℓ⁻ and B_s → ϕℓ⁺ℓ⁻ branching ratios are computed and the differential branching fractions are given as a function of the squared-momentum transfer. (paper)