After the successful completion of Run I and II of the Large Hadron Collider (LHC) the much anticipated discovery of signals of beyond-the-Standard-Model physics is still lacking. Precision tests scrutinising the Standard Model are of prime importance in its physics programme, now and in the foreseeable future. At the same time new physics searches are looking for increasingly small signals demanding more precise estimates of the Standard Model backgrounds. Run III, having commenced recently, and the High-Luminosity upgrade thereafter, will further increase the available luminosity, enlarging the statistical prowess of the recorded data in most physics regions of interest. This expansion of sensitivity in both precision measurements and new physics searches in the multi-TeV region necessitates an immense improvement of the accuracy of theoretical predictions.

Further, strongly interacting new physics signals have been largely excluded by now, putting an emphasis on weakly interacting models and their electroweak Standard Model backgrounds. This is not only true for ongoing precision LHC measurements, but all the more so for all proposed future e+e− colliders. Lacking the vast energy range of a hadron collider they focus, in one form or another, on measurements with unprecedented precision to probe the Standard Model and, possibly, expose any deviations from its predictions.

The research performed in this PhD aims to provide precision calculations for relevant processes and observables at the LHC and future colliders that are necessary to contrast and test the predictions of our current best theory, the Standard Model, against the expected high-precision experimental data. In consequence, contribution from new physics not contained in the Standard Model to such processes and observables can be analysed and interpreted either as discoveries or more and more stringent exclusion limits.