High-precision analyses of supersymmetry parameters aim at reconstructing the fundamental supersymmetric theory and its breaking mechanism. A well defined theoretical framework is needed when higher-order corrections are included. We propose such a scheme, Supersymmetry Parameter Analysis SPA, based on a consistent set of conventions and input parameters. A repository for computer programs is provided which connect parameters in different schemes and relate the Lagrangian parameters to physical observables at LHC and high energy e + e − linear collider experiments, i.e., masses, mixings, decay widths and production cross sections for supersymmetric particles. In addition, programs for calculating high-precision low energy observables, the density of cold dark matter (CDM) in the universe as well as the cross sections for CDM search experiments are included. The SPA scheme still requires extended efforts on both the theoretical and experimental side before data can be evaluated in the future at the level of the desired precision. We take here an initial step of testing the SPA scheme by applying the techniques involved to a specific supersymmetry reference point.

We improve the calculation of the supersymmetric O(α s ) QCD corrections to the decays of Higgs bosons into quarks and squarks in the Minimal Supersymmetric Standard Model. In the on-shell renormalization scheme these corrections can be very large, which makes the perturbative expansion unreliable. This is especially serious for decays into bottom quarks and squarks for large tan β. Their corrected widths can even become negative. We show that this problem can be solved by a careful choice of the tree-level Higgs boson couplings to quarks and squarks, in terms of the QCD and SUSY QCD running quark masses, running trilinear couplings A q , and on-shell left-right mixing angles of squarks. We also present numerical results for the corrected partial decay widths for the large tan β case.

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We present a detailed study of the decays of the Higgs bosons H + , H 0 , and A 0 within the Minimal Supersymmetric Standard Model including SUSY-QCD corrections. We find that the supersymmetric modestb (tt, and for large tan βbb) can dominate the H + (H 0 , A 0 ) decays in a wide range of the model parameters due to the large Yukawa couplings and mixings oft andb. Compared to the conventional modes H + → τ + ν τ , tb, and H 0 , A 0 → tt, bb, the supersymmetric modes can have an important impact on the Higgs boson searches at future colliders. *

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