Constraining the Unitarity Triangle with B →

We discuss the exclusive radiative decays B → K∗γ, B → ργ, and B → ωγ in QCD factorization within the Standard Model. The analysis is based on the heavy-quark limit of QCD. Our results for these decays are complete to next-to-leading order in QCD and to leading order in the heavy-quark limit. Special emphasis is placed on constraining the CKM-unitarity triangle from these observables. We propose a theoretically clean method to determine CKM parameters from the ratio of the B → ρlν decay spectrum to the branching fraction of B → ργ. The method is based on the cancellation of soft hadronic form factors in the large energy limit, which occurs in a suitable region of phase space. The ratio of the B → ργ and B → K∗γ branching fractions determines the side Rt of the standard unitarity triangle with reduced hadronic uncertainties. The recent Babar bound on B(B0 → ρ0γ) implies Rt < 0.81 (ξ/1.3), with the limiting uncertainty coming only from the SU(3) breaking form factor ratio ξ. This constraint is already getting competitive with the constraint from Bs-B̄s mixing. Phenomenological implications from isospinbreaking effects are briefly discussed.