PHACT : Helicity amplitudes for present and future colliders
Alessandro Ballestrero
TL;DR
The paper tackles the challenge of computing helicity amplitudes for processes with many external fermions at high-energy colliders. It introduces PHACT, a method based on generalized spinors and tau-matrix representations to systematically construct amplitudes and reduce diagram counts. It describes how PHACT generates optimized Fortran code and is integrated into WPHACT and SIXPHACT Monte Carlo programs, enabling high-precision predictions for four- and six-fermion final states. The approach provides fast, modular computations suitable for current LEP2/Linear Collider studies and future LHC physics.
Abstract
Helicity amplitudes calculations with the program PHACT are explained. Some examples of their application in WPHACT and SIXPHACT MC's are given.