Theory of Rare B Decays

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We discuss some selected topics in rare B decays in the context of the standard model and compare theoretical estimates with available data. Salient features of the perturbative-QCD and power corrections in the decay rate for B → Xₛ + γ are reviewed and this framework is used to determine the Cabibbo-Kobayashi-Maskawa (CKM) matrix element | Vts |. We review estimates of the ratio Rₖ* ≡ Γ(B → K* + γ)/Γ(B → Xₛ + γ) in a number of theoretical models, which give a consistent account of this quantity. Issues bearing on the photon energy spectrum in B → Xₛ + γ are also discussed. The CKM-suppressed decays B → Xd + γ, B± → ρ± + γ, and B⁰ → (ρ⁰, ω) + γ are reviewed with particular emphasis on the long-distance contributions in the exclusive decays. The impending interest in these decays in determining the parameters of the CKM matrix is emphasized. Finally, the semileptonic decays B → Xₛ ℓ+ ℓ- are also discussed in the context of the SM.