Singular and Regular Gauges in Soft Collinear Effective Theory: The Introduction of the New Wilson Line T

Understand

Gauge invariance in soft-collinear effective theory (SCET) is discussed in regular (covariant) and singular (light-cone) gauges.

• It is argued that SCET, as it stands, is not capable to define in a gauge invariant way certain non-perturbative matrix elements that are an integral part of many factorization theorems.
• Those matrix elements involve two quark or gluon fields separated not only in light-cone direction but also in the transverse one.
• This observation limits the range of applicability of SCET.