Calculating two- and three-body decays with FeynArts and FormCalc

The Feynman diagram generator FeynArts and the computer algebra program FormCalc allow for an automatic computation of 2→ 2 and 2→ 3 scattering processes in High Energy Physics. We have extended this package by four new kinematical routines and adapted one existing routine in order to accomodate also twoand three-body decays of massive particles. This makes it possible to compute automatically twoand three-body particle decay widths and decay energy distributions as well as resonant particle production within the Standard Model and the Minimal Supersymmetric Standard Model at the treeand loop-level. The use of the program is illustrated with three standard examples: h → bb̄, μ → eν̄eνμ, and Z → νeν̄e.