Off-Shell Effects for Top Quark Production at Hadron Colliders.

A good description of processes involving the production and decay of top quarks is crucial to phenomenology at the Tevatron and LHC. In this thesis, a general method constructed using ideas from Effective Theories is presented, allowing predictions to be made for differential observables that importantly include the effects of non-zero top quark virtuality. Calculations using this method can be significantly simpler than those in standard perturbation theory and its use enables the identification of potentially important structures in the amplitudes. The method is applied to the example of top-pair production for a realistic experimental setup at the Tevatron. A number of observables are studied and an evaluation of off-shell effects is given. The latter tend to be small in general but do become enhanced in regions near kinematical boundaries for distributions that are sensitive to the invariant mass of top quarks.