Narrow Results

We investigate the nature of power corrections and infrared renormalon singularities in large-β₀ approximation. We argue that the power correction associated with a renormalon pole singularity should appear at O(1), in contrast to the renormalon ambiguity appearing at O(1/β₀), and give an explanation why the leading order renormalon singularities are generically poles.

Event shapes have long been used to extract information about hadronic final states and the properties of QCD, such as particle spin and the running coupling. Recently, a family of event shapes, the angularities, has been introduced that depends on a continuous parameter. This additional parameter-dependence further extends the versatility of event shapes. It provides a handle on nonperturbative power corrections, on non-global logarithms, and on the flow of color in the final state.

Two-jet event shape distributions, traditionally studied in the language of perturbative QCD, can be described naturally in soft-collinear effective theory. In this language, we demonstrate factorization of event shape distributions into perturbatively-calculable hard and jet functions and nonperturbative soft functions, and show how the latter contribute universal shifts to the mean values of various event shape distributions. Violations of universality in shifts of higher moments can give information on correlations of energy flow in soft radiation.

In this paper we discuss calculation of power corrections to the transverse momentum dependent (TMD) factorization which describes production of a particle with small transverse momentum in a hadron-hadron collision. As an example we consider power corrections to the TMD factorization formula for Z-boson production. We demonstrate that in the leading order in N_c power corrections can be expressed in terms of leading-twist TMDs which is a consequence of QCD equations of motion.