Technische Universit¨at Mu¨nchenMax-Planck-Institut fu¨r Physik(Werner-Heisenberg-Institut)Precision Calculations for the Decay ofHiggs Bosons in the MSSMJianhui ZhangVollst¨andiger Abdruck der von der Fakult¨at fu¨r Physikder Technischen Universit¨at Mu¨nchenzur Erlangung des akademischen Grades einesDoktors der Naturwissenschaften (Dr. rer. nat.)genehmigten Dissertation.Vorsitzender: Univ.-Prof. Dr. L. OberauerPru¨fer der Dissertation: 1. Hon.-Prof. Dr. W. F. L. Hollik2. Univ.-Prof. Dr. A. J. BurasDie Dissertation wurde am 22.10.2008bei der Technischen Universit¨at Mu¨nchen eingereicht unddurch die Fakult¨at fu¨r Physik am 21.01.2009 angenommen.AbstractPrecision calculations are required for the verification of the standard model (SM) and serveas a useful tool for probing and disentangling new physics beyond the SM. In this thesis weconcentrateontheextensionoftheSMwithsupersymmetry,i.e. theminimalsupersymmetricextensionof thestandardmodel(MSSM) andinvestigate thedecay processesofHiggs bosons0within this model. At tree-level, the light CP-even MSSM Higgs boson,h , becomes SM-likewhen the other Higgs bosons get heavy. Thus it is of particular interest to investigate theimpact of higher order corrections. We present the complete one-loop electroweak radiative0corrections to the decay of h to four fermions via gauge boson pair, the results are furtherimproved by currently available two-loop corrections to the Higgs boson self energies.