  In this Thesis we have investigated some effects appearing in top quark
observables in the framework of the Minimal Supersymmetric Standard Model
(MSSM). We have computed the radiative corrections to some top quark
observables, using the on-shell renormalization scheme, and with a physically
motivated definition of the tan(beta) parameter. Introductory chapters deal
with the MSSM, its renormalization, and the on-shell prescription. In the next
chapters we have computed the SUSY-EW corrections (and some SUSY-QCD
corrections) to: the non-standard top quark decay partial width \Gamma(t->H+
b); the FCNC top quark decay width \Gamma(t-> c h) (h=h^0,H^0,A^0); and the
non-standard top quark production through sbottom decays \Gamma(sbottom -> t
\chi^-). We have investigated the consequences of the corrections to
\Gamma(t->H^+ b) in the interpretation of the present Tevatron data. Our
general conclusion is that the supersymmetric strong and electroweak radiative
corrections can be very important in the top/bottom-Higgs super-sector of the
MSSM. Therefore, it is necessary to account for these corrections in the
theoretical computation of the high energy physics observables, otherwise
highly significant information on the potentially underlying SUSY dynamics
could be missed. This is true, not only for the future experiments at the LHC
and the LC, but also for the present Run I data (and the Run II data around the
corner) at the Fermilab Tevatron collider.
