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Manuscript Title: HELAC: a package to compute electroweak helicity amplitudes.
Authors: A. Kanaki, C.G. Papadopoulos
Program title: HELAC
Catalogue identifier: ADMS_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 132(2000)306
Programming language: Fortran.
Computer: ALPHA workstation, HP workstation, IBM workstation.
Operating system: Unix.
Keywords: Elementary particle physics, Quantum Chromodynamics, Automatic evaluation of helicity amplitudes, Dyson-Schwinger equations, Recursive algorithms.
Classification: 11.5.

Nature of problem:
A substantial part of particle phenomenology nowadays is based upon our ability to study efficiently processes involving a relatively large number of particles. This requires efficient algorithms for matrix element calculation and phase space generation and integration. As far as the matrix element calculation is concerned, the traditional approach utilizes standard Feynman graph representation of the scattering amplitude, resulting to a computational cost that grows asymptotically as n!, where n is the number of particles involved in the process.

Solution method:
As alternative recursive algorithms based on Schwinger-Dyson equations lead asymptotically to a much lower growth of the computational cost, namely a**n, where a ~ 3, it is the aim of this paper to present such an algorithm as well as the corresponding Fortran code which allows the computation of any tree-order electroweak amplitude.