Subleading power corrections in radiative leptonic B decay

I discuss the two-particle subleading power corrections in radiative leptonic B→γℓν decay at next-to-leading order in αs with the dispersion approach. Employing the method of regions, factorization of the B→γ⁎ form factors is demonstrated explicitly, at one loop, for a space-like hard-collinear photon. The two-particle soft (end-point) contribution is shown to be suppressed by one power of Λ/mb, in the heavy quark limit, compared with the leading power contribution computed from QCD factorization. I further report the recent calculation on the three-particle subleading power contribution to the on-shell B→γ form factors at tree level and demonstrate that the “soft” and the “hard” three-particle corrections are of the same power, in contrast to the two-particle counterparts, as already speculated from the rapidity divergence in the corresponding factorization formulae. Phenomenological implications of the subleading power contributions to the B→γℓν amplitude are also addressed in detail, focusing on the determination of the inverse moment of the leading-twist B-meson distribution amplitude.