Beyond leading-order corrections to bar{B} -> X_s gamma at large tan beta: the charged-Higgs contribution
Abstract
Among the O(alpha_s tan beta) contributions to the Wilson coefficients C_7 and C_8, relevant for the decay bar{B} -> X_s gamma, those induced by two-loop diagrams with charged-Higgs-boson exchange and squarks-gluino corrections are calculated in supersymmetric models at large tan beta. The calculation of the corresponding Feynman integrals is exact, unlike in previous studies valid when the typical supersymmetric scale M_SUSY is sufficiently larger than the electroweak scale m_weak (\sim m_W, m_t) and the mass of the charged-Higgs boson m_{H^\pm}. Therefore, the results presented here can be used for any value of the various supersymmetric masses. These results are compared with the approximated ones existing in the literature, which are at the zeroth order in the expansion parameter (m_weak^2,m_H^2)/M_SUSY^2, and with the results of two new approximated calculations, in which the first and second order in the same expansion parameter are retained, respectively. This comparison allows to assess whether the results of these three approximated calculations can be extended beyond the range of validity for which they have been derived, i.e. whether they can be used for m_H^2 \gtap M_SUSY^2 and/or M_SUSY^2 \sim m_weak^2.Keywords
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