HELAC-PHEGAS: automatic computation of helicity amplitudes and cross sections

HELAC-PHEGAS is a FORTRAN based package that is able to compute automatically and efficiently tree-level helicity amplitudes and cross sections for arbitrary scattering processes within the standard electroweak theory and QCD. The algorithm for the amplitude computation, HELAC, exploits the virtues of the Dyson-Schwinger equations. A colour representation that facilitates both the summation over colours and the extraction of the colour-connection information, is implemented. The phase-space generation algorithm PHEGAS, constructs all possible kinematical mappings dictated by the amplitude under consideration. Combined with multichannel self-optimized Monte Carlo integration it results in efficient cross section evaluation and event generation. (author)