General subtraction method for numerical calculation of one-loop QCD matrix elements

We present a subtraction scheme for eliminating the ultraviolet, soft, andcollinear divergences in the numerical calculation of an arbitrary one-loop QCDamplitude with an arbitrary number of external legs. The subtractions consistof local counter terms in the space of the four-dimensional loop momentum. Theultraviolet subtraction terms reproduce MSbar renormalization. The key point inthe method for the soft and collinear subtractions is that, although thesubtraction terms are defined graph-by-graph and the matrix element is alsocalculated graph-by-graph, the sum over graphs of the integral of each thesubtraction term can be evaluated analytically and provides the well knownsimple pole structure that arises from subtractions from real emission graphs,but with the opposite sign.Comment: 38 pages, 10 figures, axodraw styl