In this paper
we consider mixed two-loop electroweak corrections to the top quark
propagator in the Standard Model.
In particular, we compute the on-shell renormalization constant
for the mass and wave function, which constitute building blocks for
many physical processes.
The results are expressed in terms of master integrals. For the latter
practical approximations are derived.
In the case of the mass renormalization constant we find agreement with the
results in the literature.