  Motivated by the results of the electroweak precision experiments, studies of
two-loop self-energy Feynman diagrams are performed. An algebraic method for
the reduction of all two-loop self-energies to a set of standard scalar
integrals is presented. The gauge dependence of the self-energies is discussed
and an extension of the pinch technique to the two-loop level is worked out. It
is shown to yield a special case of the background-field method which provides
a general framework for deriving Green functions with desirable theoretical
properties. The massive scalar integrals of self-energy type are expressed in
terms of generalized multivariable hypergeometric functions. The imaginary
parts of these integrals yield complete elliptic integrals. Finally,
one-dimensional integral representations with elementary integrands are derived
which are well suited for numerical evaluation.
