Higgs Particles in the Standard Model and Supersymmetric Theories
  This thesis presents a theoretical analysis of the properties of the Higgs bosons in the Standard Model (SM) and the minimal supersymmetric extension (MSSM), which can be investigated at the LHC and $e^+e^-$ linear colliders. The final goal is the reconstruction of the Higgs potential and thus the verification of the Higgs mechanism. MSSM Higgs boson production processes at future $\gamma\gamma$ colliders are calculated in several decay channels. Heavy scalar and pseudoscalar Higgs bosons can be discovered in the $b\bar{b}$ final state in the investigated mass range 200 to 800 GeV for moderate and large values of $\tan\beta$. The $\tau^+\tau^-$ channel provides a heavy Higgs boson discovery potential for large values of $\tan\beta$. Several mechanisms that can be exploited at $e^+e^-$ linear colliders for the measurement of the lifetime of a SM Higgs boson in the intermediate mass range are analysed. In the $WW$ mode, the lifetime of Higgs scalars with masses below $\sim 160$ GeV can be determined with an error less than 10%. The reconstruction of the Higgs potential requires the measurement of the Higgs self-couplings. The SM and MSSM trilinear Higgs self-couplings are accessible in double and triple Higgs production. A theoretical analysis is presented in the relevant channels at the LHC and $e^+e^-$ linear colliders. For high luminosities, the SM trilinear Higgs self-coupling can be measured with an accuracy of 20% at a 500 GeV $e^+e^-$ linear collider. The MSSM coupling among three light Higgs bosons has to be extracted from continuum production. The other trilinear Higgs couplings are measurable in a restricted range of the MSSM parameter space. At the LHC, the $Hhh$ coupling can be probed in resonant decays. 
M.M. Muhlleitner