Top pair production at hadron colliders in non-minimal standard models

The cross section of top pair production in hadronic collisions to script O sign(αα²_s) is calculated within the General 2-Higgs Doublet Model and the Minimal Supersymmetric Standard Model. At the parton level the script O sign(α) one-loop corrections to the main production mechanisms, qq̄ → tt̄ and gg → tt̄, significantly modify the Born cross sections: in the threshold region √ŝ ≳ 2m_t they are enhanced up to 50% and with increasing cm energy √ŝ, they can be reduced by up to the same order of magnitude. In a wide range of the parameter space of the models under consideration the observable hadronic cross sections for top pair production at the Tevatron pp̄ → tt̄X and at the LHC pp → tt̄X are typically reduced by several percent (≲ 10%) compared to the lowest order result. In special regions of the parameter space, that is in the vicinity of the threshold for the top quark decay t → b H⁺ ; t̃ X̃⁰, the radiative corrections are considerably enhanced, comparable in size to QCD effects.