The soft-gluon current at one-loop order

We study the soft limit of one-loop QCD amplitudes and we derive the proces s-independent factorization formula that controls the singular behaviour in this limit. This is obtained from the customary eikonal factorization form ula valid at tree (classical) level by introducing a generalized soft-gluon current that embodies the quantum corrections. We compute the explicit exp ression of the soft-gluon current at one-loop order. It contains purely non -abelian correlations between the colour charges of each pair of hard-momen tum partons in the matrix element. This leads to colour correlations betwee n (two and) three hard partons in the matrix element squared. Exploiting co lour conservation, we recover QED-like factorization for the square of the matrix elements with two and three hard partons. (C) 2000 Elsevier Science B.V. All rights reserved.