SCET, QCD and Wilson Lines

TL;DR

This paper shows that SCET can be reformulated as multiple decoupled QCD sectors connected by Wilson lines, simplifying the treatment of soft and collinear interactions in high-energy processes.

Contribution

The authors demonstrate that the collinear expansion in SCET is unnecessary and that the theory can be expressed as decoupled QCD copies linked by Wilson lines, simplifying its structure.

Findings

Reformulation of SCET as multiple decoupled QCD sectors.

Interactions are represented by QCD fields coupled to Wilson lines.

Illustrated with dijet production and B->X_s + gamma examples.

Abstract

Soft Collinear Effective Theory (SCET) is an effective field theory which describes the interactions of low invariant mass jets which are highly boosted with respect to one another. In the standard formulation of SCET, the effective Lagrangian for collinear fields is expanded in inverse powers of the energy. At leading order this leads to manifest decoupling of soft and collinear degrees of freedom; however, subleading terms in the effective Lagrangian violate this manifest decoupling. In this paper we point out that the collinear expansion in the SCET Lagrangian is unnecessary, and that the SCET Lagrangian may instead be written as multiple decoupled copies of QCD. The interactions between the sectors in full QCD are reproduced in the effective theory by an external current consisting of QCD fields coupled to Wilson lines. We illustrate this picture with two examples: dijet production and B->X_s + gamma.