Next-to-leading power corrections to event-shape variables

We investigate the origin of next-to-leading power (NLP) corrections to the event shapes’ thrust and c-parameter, at next-to-leading order. For both event shapes, we trace the origin of such terms in the exact calculation, and compare with a recent approach involving the eikonal approximation and momentum shifts that follow from the Low–Burnett–Kroll–Del Duca (LBKD) theorem. We assess the differences both analytically and numerically. For the c-parameter both exact and approximate results are expressed in terms of elliptic integrals, but near the elastic limit it exhibits patterns similar to the thrust results.