Two-loop quark and gluon form factors in dimensional regularisation

We compute the two-loop corrections to the massless quark form factor gamma* -> qq and gluon form factor H -> qq to all orders in the dimensional regularisation parameter epsilon = (4 - d)/2. The two-loop contributions to the form factors are reduced to linear combinations of master integrals, which are computed in a closed form, expressed as Gamma-functions and generalised hypergeometric functions of unit argument. Using the newly developed HypExp-package, these can be expanded to any desired order, yielding Laurent expansions in epsilon. We provide expansions of the form factors to order epsilon(2), as required for ultraviolet renormalisation and infrared factorisation of the three-loop form factors. (c) 2005 Elsevier B.V. All rights reserved.