Radiative corrections to $e^+ e^- \to H^+ H^-$: THDM versus MSSM

One loop radiative corrections to $e^+e^-\to H^+ H^-$ are considered at future linear collider energies, in the general type II Two Higgs Doublet Model (THDM) and in the Minimal Supersymmetric Standard Model (MSSM). To make easy the comparison between THDM and MSSM, we have introduced a quasi-SUSY parametrisation which preserves all the tree-level Higgs mass-sum-rules of the MSSM, and involves just 3 free parameters in the Higgs sector (instead of 7 in the general THDM) and comprises the MSSM as a particular case. The model-independent soft photon contribution is isolated and shown to be substantial. Important effects come also from the contribution of the model dependent $h^0 H^+ H^-$ and $H^0 H^+ H^-$ vertices to the final state. In the MSSM, the contribution of the Higgs sector is moderate (a few percent) while in the THDM and both for small and large tan$\beta$ important effects ($\sim +30%$) can be found.