QCD corrections to B̄→Xd,sνν̄, B̄d,s→l+l−, K→πνν̄ and KL→μ+μ− in the MSSM Original Research Article

We compute for the first time QCD corrections to the rare decays B̄→Xd,sνν̄, B̄d,s→l+l−, K→πνν̄ and KL→μ+μ−, where l=e or μ, in the context of a supersymmetric extension of the Standard Model (SM) with minimal flavour violation and new operators, in addition to those present in the SM. Assuming that the gluino is heavy, we consider an effective theory which consists of charged and neutral Higgs particles, charginos and squarks. We evaluate the QCD corrections to box and Z0-penguin diagrams with top-quark, charged Higgs boson, chargino and squark exchanges, as well as to neutral Higgs boson penguin diagrams. We provide a compendium of analytic formulae for the Wilson coefficients, which are valid for arbitrary values of tanβ (the ratio of the vacuum expectation values of the two Higgs fields) except for the case of the neutral Higgs-boson contributions. These contributions have been obtained at large tanβ, which may compensate for the inevitable suppression by the masses of the light leptons in decays based on the b→s(d)l+l− transition. We investigate the dependence of the various branching ratios on the renormalization scale μ, which is the main theoretical uncertainty in the short-distance calculation. We find that the μ dependence of the branching ratios is considerably reduced once the QCD corrections are taken into account. The contributions of new operators are found to be dominant at large tanβ in B̄d,s→μ+μ− while they are subleading in B̄→Xd,sνν̄ and completely negligible in kaon decays.