  New results for the complete one-loop contributions to the masses and mixing
effects in the Higgs sector are obtained for the MSSM with complex parameters
using the Feynman-diagrammatic approach. The full dependence on all relevant
complex phases is taken into account, and all the imaginary parts appearing in
the calculation are treated in a consistent way. The renormalization is
discussed in detail, and a hybrid on-shell/DRbar scheme is adopted. We also
derive the wave function normalization factors needed in processes with
external Higgs bosons and discuss effective couplings incorporating leading
higher-order effects. The complete one-loop corrections, supplemented by the
available two-loop corrections in the Feynman-diagrammatic approach for the
MSSM with real parameters and a resummation of the leading (s)bottom
corrections for complex parameters, are implemented into the public Fortran
code FeynHiggs2.5. In our numerical analysis the full results for the
Higgs-boson masses and couplings are compared with various approximations, and
CP-violating effects in the mixing of the heavy Higgs bosons are analyzed in
detail. We find sizable deviations in comparison with the approximations often
made in the literature.
