Speaker
Description
Infrared singular factors originating from the QCD factorisation of scattering amplitudes in soft and collinear limits play an important role both in the organisation and in the calculation of the higher-order contributions to hard scattering cross sections. In this talk I will report on recent work for the evaluation of collinear contributions to QCD resummations of hard scattering observables. We start from the factorisation of squared amplitudes in the collinear limit and introduce fully differential collinear functions that have a process-independent structure. These collinear functions can then be integrated over the corresponding observable-dependent phase space to obtain the logarithmically-enhanced contributions to the observable of interest. For transverse-momentum dependent observables, we show how collinear functions can be defined without introducing what is known as rapidity divergences in the literature. We present analytical expressions for the collinear functions up to next-to-next-to-leading order in perturbation theory.