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 treeorder 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. The phase-space generation algorithm, PHEGAS, constructs all possible kinematical mappings dictated by the amplitude under consideration. Combined with mutichannel self-optimized Monte Carlo integration it results to efficient cross section evaluation.