  In the case of heavy-to-light weak meson transitions, a Quark Model
derivation leads to very general relations between the form factors that
parametrize the hadronic matrix elements. We investigate to what extent these
form factor relations remain a good approximation, beyond the Quark Model.
  In heavy-to-light pseudoscalar-to-vector meson transitions, a simple argument
shows that the V-A structure of the weak interaction leads to a strong
suppression of the helicity h=+1 amplitude - an effect that has been confirmed
experimentally by the CLEO Collaboration, with a full angular analysis of the B
-> K* J/psi decay. We show that the theoretical predictions, in terms of the
hadronic form factors, can accommodate the suppression of the h=+1 amplitude,
only if the Quark Model relations are verified. Moreover, the form factor
relations also allow us to predict the ratio of the two remaining helicity
amplitudes, with h=0 and h=-1; here too, there is excellent agreement with the
CLEO data for the B -> K* J/psi decay. In the future, similar experimental
tests can be carried out, with a few advantages, using the semileptonic decay B
-> rho l- nu_l.
  The Quark Model relations can also be tested against the predictions for the
hadronic form factors, from the more powerful theoretical methods of Lattice
QCD and Light Cone Sum-Rules. The excellent agreement points once again to the
validity of the form factor relations, beyond the Quark Model framework where
they were derived.
