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We present a systematical study of two-body and three-body charmless baryonic B decays. The branching ratios for two-body modes are in general very small, typically less than 10 Ϫ6 , except that B(B Ϫ →p⌬ ϪϪ ) ϳ1ϫ10 Ϫ6 . In general, B →N⌬ ϾB →NN due to the large coupling constant for ⌺ b →B⌬. For three-body modes we focus on octet baryon final states. The leading three-dominated modes are B 0 →pn Ϫ ( Ϫ ), np ϩ ( ϩ ) with a branching ratio of order 3ϫ10 Ϫ6 for B 0 →pn Ϫ and 8ϫ10 Ϫ6 for B 0 →pn Ϫ . The penguin-dominated decays with strangeness in the meson, e.g., B Ϫ →pp K Ϫ( * ) and B 0 →pn K Ϫ( * ) , nn K 0( * ) , have appreciable rates and the NN mass spectrum peaks at low mass. The penguin-dominated modes containing a strange baryon, e.g., B 0 →⌺ 0 p ϩ , ⌺ Ϫ n ϩ , have branching ratios of the order of (1 -4)ϫ10 Ϫ6 . In contrast, the decay rate of B 0 →⌳p ϩ is smaller. We explain why some of the charmless three-body final states in which baryon-antibaryon pair production is accompanied by a meson have a larger rate than their two-body counterparts: either the pole diagrams for the former have an antitriplet bottom baryon intermediate state, which has a large coupling to the B meson and the nucleon, or they are dominated by the factorizable external W-emission process.

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We have presented a detailed study of twist-2 and twist-3 light-cone distribution amplitudes of 1 3 P 1 and 1 1 P 1 axial-vector mesons, based on QCD conformal partial wave expansion. Applying equations of motion, the twist-three two-parton light-cone distribution amplitudes can be expressed in terms of leading-twist and twist-three three-parton light-cone distribution amplitudes. The relevant G-parity invariant and violating parameters, containing the corrections due to the SU(3) breaking effects, are evaluated from the QCD sum rule method. The results for axial-vector decay constants of 1 3 P 1 states are presented. The values of tensor decay constants and Gegenbauer moments of the leading twist distribution amplitudes for 1 1 P 1 states are updated. Using Gell-Mann-Okubo mass formula, the mixing angle for the f 8 and f 1 of 1 3 P 1 states is θ3 P 1 ∼ 38 • , and that for h 8 and h 1 of 1 1 P 1 states is θ1 P 1 ∼ 10 • . The detailed properties for physical states f 1 (1285), f 1 (1420), h 1 (1170), and h 1 (1380) are given. Assuming the mixing angle between K 1A and K 1B to be θ K = 45 • or −45 • , we also give the detailed study for K 1 (1270) and K 1 (1400). Using the conformal partial wave expansion, we obtain the models for light-cone distribution amplitudes, containing contributions up to conformal spin 9/2. It is interesting to note that some distribution amplitudes have significant asymmetric behaviors, which should be phenomenologically attractive.