Large tan beta SUSY QCD corrections to B -> Xₛ gamma

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The charged-Higgs boson contributions to the Wilson coefficients C₇ and C₈, relevant for the decay B -> Xₛ gamma, are discussed in supersymmetric models at large tan beta. These contributions receive two-loop O(alphaₛ tan beta) corrections by squark-gluino subloops, which are possibly large and nondecoupling in the limit of heavy superpartners. In previous studies, the relevant two-loop Feynman integrals were approximated by using an effective two-Higgs-doublet lagrangian. However, this approximation is theoretically justified only when the typical supersymmetric scale MₛUSY is sufficiently larger than the electroweak scale mweak (mW,mₜ) and the mass of the charged-Higgs boson mₕ±. Here we evaluate these two-loop integrals exactly and compare the results with the existing, approximated ones. We then examine the validity of this approximation beyond the region where it has been derived, i.e. for mₕ MₛUSY and/or MₛUSY mweak.