The singular behaviour of QCD amplitudes at two-loop order

We discuss the structure of infrared singularities in on-shell QCD amplitudes at two-loop order. We present a,general factorization formula that controls all the epsilon-poles of the dimensionally regularized amplitudes, The dependence on the regularization scheme is considered and the coefficients of the 1/epsilon(+),1/epsilon(3) and 1/epsilon(2) poles are explicitly given in the most general case. The remaining single-pole contributions are also explicitly evaluated in the case of amplitudes with a <q(q)over bar> pair. (C) 1998 Elsevier Science B.V. All rights reserved.