Universality of 1/Q corrections revisited

TL;DR

Addresses universality of 1/Q power corrections for event shapes in e+e- annihilation by performing an exact two-loop abelian calculation of the C parameter within the dispersive/massive-gluon framework and comparing to the abelian Milan factor. Demonstrates a simple proportionality between the leading 1/Q corrections of C and the longitudinal cross section in the soft region, and confirms this relation for the full two-loop abelian contribution. Finds a numerical mismatch with earlier Milan-factor estimates that is discussed and, after corrections, supports universality of the Milan factor for these observables. Highlights the method's potential extension to other event shapes and to non-abelian contributions, and notes the relevance for distributions and DIS.

Abstract

We provide an exact analytical calculation at the two-loop level in the abelian limit of the leading power correction for the C parameter in e+e- annihilation. We compare our results to the numerical value obtained employing the soft approximation, the abelian part of the Milan factor. We demonstrate that a simple proportionality holds between the leading power corrections to the C parameter and to the longitudinal cross section in the soft region, and we verify that this proportionality holds for the full two-loop abelian contribution computed here. We comment on the possibility of extending this technique to other event shape variables and distributions, as well as to the non-abelian contributions.