Reparameterization invariance for collinear operators

We discuss restrictions on operators in the soft-collinear effective theory (SCET) which follow from the ambiguity in the decomposition of collinear momenta and the freedom in the choice of light-like basis vectors n and (n) over bar. Invariance of SCET under small changes in n and/or (n) over bar implies a symmetry of the effective theory that constrains the form of allowed operators with collinear fields. The restrictions occur at a given order in the power counting as well as between different orders. As an example, we present the complete set of higher order operators that are related to the collinear quark kinetic term. (C) 2002 Elsevier Science B.V. All rights reserved.