Form factors for B → j1 j2 decays into two currents in QCD

We discuss the general properties of the B-meson decay form factors F(q(2), q'(2)), describing B-meson decays induced by two currents, e.g., B decays into four leptons in the final state. We study the analytic properties of these complicated objects and identify those regions of q(2) and q'(2), where perturbative QCD can be applied for obtaining predictions for the physical form factors.