Charged Higgs Boson Production in Bottom-Gluon Fusion

We compute the complete next-to-leading order SUSY-QCD corrections for the associated production of a charged Higgs boson with a top quark via bottom-gluon fusion. We investigate the applicability of the bottom parton description in detail. The higher order corrections can be split into real and virtual corrections for a general two Higgs doublet model and into additional massive supersymmetric loop contributions. We find that the perturbative behavior is well under control. The supersymmetric contributions consist of the universal bottom Yukawa coupling corrections and non-factorizable diagrams. Over most of the relevant supersymmetric parameter space the Yukawa coupling corrections are sizeable, while the remaining supersymmetric loop contributions are negligible. I. HIGGS PHYSICS AT THE LHC In the near future the CERN Large Hadron Collider (LHC) will be the appropriate tool to look for physics beyond the Standard Model and to determine its properties. The capabilities of the LHC beyond being a pure discovery machine become increasingly important at energy scales which are hard to access at a Linear Collider. The combined LEP precision measurements [1] suggest the existence of a light Higgs boson. In the case of a single Standard Model Higgs boson the LHC promises multiple coverage for any Higgs boson mass, which will enable us to measure its different decay modes and extract the couplings [2–4]. In the case of a supersymmetric Higgs sector this coverage becomes less impressive. This is a direct consequence of the structure of the Higgs sector: while the Minimal Supersymmetric Standard Model (MSSM) predicts a light Higgs boson it also predicts an enhancement of the coupling to down-type fermions, at the expense of the branching fractions to gauge bosons. This enhancement is an outcome from the two Higgs doublet structure in the MSSM: one doublet is needed to give mass to the up-type, the other one to the down-type fermions. The vacuum expectation values of the two doublets are different, parameterized by tan β = v2/v1. The Yukawa coupling to the down-type fermions is essentially enhanced by tanβ, while the coupling to uptype fermions is suppressed by the same factor. In addition to a light scalar Higgs boson the two Higgs doublet model includes a heavy scalar, a pseudoscalar, and a charged Higgs boson. None of these additional particles have a mass bounded from above, apart from triviality or unitarity bounds. On the contrary, for a large pseudoscalar mass these three additional particles all become heavy and almost mass degenerate.