Top-quark physics at hadron colliders

Top-quark pair production is one of the fundamental processes under investigation at currenthadron-collider experiments and plays an important role in various phenomenological applicationswithin the Standard Model as well as in the search for new-physics contributions. Therefore, a lot of effort is put into the further improvement of its theoretical description tocope with the continuing progress in experimental precision, in particular in the light of thecurrent and upcoming runs of the Large Hadron Collider. For a long time, the state-of-thearttheoretical predictions consisted of a fixed-order perturbative evaluation at next-to-leadingorder (NLO) in the strong coupling possibly refined by an all-order treatment of dominantradiation effects, either through parton showers or soft-gluon resummation. However, for thetotal inclusive production cross section in the recent years the first calculations at genuinenext-to-next-to-leading order (NNLO) accuracy became available, starting with the resultsfor the quark annihilation channel and soon followed by the O(alpha_s^4) contributions to the otherpartonic production modes containing at least one initial-state fermion.In this thesis, the methods and tools necessary for such an advanced perturbative analysis arepresented focusing in particular on the derivation of the two-loop virtual corrections requiredfor a completion of the NNLO gluon-fusion-channel results. In addition, the correspondingfindings are used to determine the NNLO hard matching coefficients that are of special phenomenologicalinterest in next-to-next-to-leading logarithmic soft-gluon resummation. To thisend, the soft function that appears in the theoretical description of the partonic cross sectionclose to the pair-production threshold has to be evaluated at NNLO accuracy as well. It isconveniently parametrized in terms of a singlet/octet color basis of the final-state heavy-quarksystem and describes the emission of massless partons from eikonal lines representing the hardscattering process. While the singlet case may actually be inferred from Drell-Yan production,in this thesis the NNLO soft function for color-octet production is derived.In order to extend the NNLO theoretical description of top-quark pair production also to thedifferential level, in a subsequent step the methods of the inclusive analysis are assembled intoa unified Monte-Carlo framework that, in principle, allows for the calculation of arbitrary topquarkobservables. Afterwards, this implementation is used to compute the long-sought-forO(alpha_s^4) corrections to the top-quark forward-backward asymmetry at the Tevatron collider,which helps to finally reconcile the persisting discrepancy between theory and data. Moreover,NNLO predictions for the main kinematic distributions studied within the Tevatrontop-quark-physics program are presented and analyzed with respect to their parametric dependenceon the parton content of the initial-state (anti-)protons and the top-quark mass