SEZIONE DI ROMA III
We present our recent results for long-distance QCD effects in radiative leptonic decays Bd,s→γℓ+ℓ− (ℓ=e,μ). One encounters here two distinct types of long-distance contributions: those encoded in the B→γ transition form factors induced by the b→d,s quark currents, and those related to the charm-quark loops. We discuss constraints on the form factors imposed by gauge invariance and calculate the B→γ form factors in a broad range of the momentum transfers. We discuss in details nonfactorizable charm-loop contributions and propose a few observables which may strongly restrict the description of charmonium resonances and in the end lead to a strong reduction of the uncertainties in the theoretical predictions for B→γℓ+ℓ−.