Invariant operators in collinear effective theory

We consider processes which produce final state hadrons whose energy is much greater than their mass. In this limit interactions involving collinear fermions and gluons are constrained by a symmetry, and we give a general set of rules for constructing leading and subleading invariant operators. Wilson coefficients C(mu, (P) over bar) are functions of a label operator (P) over bar, and do not commute with collinear fields. The symmetry is used to reproduce a two-loop result for factorization in B --> D pi in a simple way. (C) 2001 Published by Elsevier Science B.V.