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Exclusive radiative B decays, B → K * γ, K 1 (1270)γ, K 1 (1400)γ and K * 2 (1430)γ, are studied in the framework of a covariant light-front quark model. The tensor form factor T 1 (q 2 ) at q 2 = 0, which is relevant to the decay B → K * γ, is found to be 0.24, substantially smaller than what expected from the conventional light-front model or light-cone sum rules. Taking into account the sizable next-to-leading order (NLO) corrections, the calculated branching ratio of B → K * γ agrees with experiment, while most of the existing models predict too large B → K * γ compared to the data. The relative strength of B → K 1 (1270)γ and B → K 1 (1400)γ rates is very sensitive to the sign of the K 1 (1270)-K 1 (1400) mixing angle. Contrary to the other models in which K 1 (1270)γ and K 1 (1400)γ rates are predicted to be comparable, it is found that one of them is strongly suppressed owing to a large cancellation between two different form factor terms. The calculated branching ratio of B → K * 2 γ is in a good agreement with experiment and this may imply the smallness of NLO corrections to this radiative decay mode.

Within the light-front framework, form factors for P→ P and P→V transitions ͑P denotes a pseudoscalar meson, V a vector meson͒ due to the valence-quark configuration are calculated directly in the entire physical range of momentum transfer. The behavior of the form factors in the infinite quark mass limit are examined to see if the requirements of heavy-quark symmetry are satisfied. We find that the Bauer-Stech-Wirbel-type light-front wave function fails to give a correct normalization for the Isgur-Wise function at zero recoil in P→V transition. Some of the P→V form factors are found to depend on the recoiling direction of the daughter mesons relative to their parents. Thus the inclusion of the nonvalence contribution arising from quark-pair creation is mandatory in order to ensure that the physical form factors are independent of the recoiling direction. The main feature of the nonvalence contribution is discussed. ͓S0556-2821͑97͒06503-X͔

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