[eng] It has been almost fifteen years ago that the top quark, the heaviest and most intriguing among the six known quarks, was observed at the Tevatron experiments at Fermilab. Some of its properties, such as the mass and the production cross sections are by now quite well known. Other important aspects, however, such as the top quark invariant mass distribution, the structure of the tWb coupling, the single top cross sections, are still subject of an intense research activity. As more data will become available and with the start-up of the LHC more precise measurements will become possible. To compare the observed data with the Standard Model (SM) and to search for effects that cannot be explained within this theory, detailed predictions are needed.
In this thesis new measurements are proposed and improvements to existing predictions are presented. First, the top quark pair invariant mass distribution within the SM is studied as well as the effects of general "model independent" new physics resonances that affect this distribution. Second, a method to set model independent bounds on the third row of the CKM matrix is proposed based on both indirect and direct measurements. Third, a new next-to-leading order prediction for t-channel single top cross section is presented in detail that allows for the first time to describe reliably some key features of the production mechanism.