Universality of 1/Q corrections to jet-shape observables rescued

TL;DR

The paper investigates whether leading $1/Q$ power corrections to jet-shape observables, such as thrust, are universal once two-loop effects are included. Using a dispersive framework with the CMW scheme, it isolates naive inclusive contributions and two-loop non-inclusive and inclusive corrections to obtain a refined thrust radiator. It demonstrates that the leading power correction gets rescaled by a calculable factor $1+r_T$, with $r_T$ receiving substantial two-loop contributions predominantly from inclusive corrections, and a smaller but negative non-inclusive piece. The results reinforce the notion that the universal soft-gluon structure and running coupling underpin power corrections, even though their magnitudes depend on the observable via the two-loop corrections, thereby preserving universality in a refined sense and guiding future analyses of other jet observables.

Abstract

We address the problem of potential non-universality of the leading 1/Q power corrections to jet shapes emerging from the non-inclusive character of these observables. We consider the thrust distribution as an example and analyse the non-inclusive contributions which emerge at the two-loop level. Although formally subleading in $\as$, they modify the existing na{\"ı}ve one-loop result for the expected magnitude of the power term by a factor of order unity. Such a promotion of a subleading correction into a numerical factor is natural since the non-perturbative power terms are explicitly proportional to powers of the QCD scale $Λ$ which can be fixed precisely only at the two-loop level. The ``jet-shape scaling factor'' depends on the observable but remains perturbatively calculable. Therefore it does not undermine the universal nature of 1/Q power corrections, which remain expressible in terms of the universal running coupling and universal soft-gluon emission.