Reliable predictions in exclusive rare B decays

We discuss the relations between form factors for B→ K^∗γ and B→ ϱe ν which follow from static heavy quark symmetry methods plus SU(3). We discuss carefully the hard perturbative QCD corrections which could invalidate these results and find that the dominant perturbative corrections are ones which respect the static symmetry predictions, and in addition that the perturbative corrections are small compared to soft contributions. We show that there is a special kinematic point in B→ ϱe ν that involves the same combination of form factors as in B→ K^∗γ , thus allowing a prediction of the ratio of rates which is largely free from hadronic uncertainties.