Eur. Phys. J. C 71, 1529 (2011)
https://doi.org/10.1140/epjc/s10052-010-1529-6

HELAS and MadGraph with spin-3/2 particles

¹ KEK Theory Center, and Sokendai, Tsukuba, 305-0801, Japan
² Theoretische Natuurkunde and IIHE/ELEM, Vrije Universiteit Brussel, and International Solvay Institutes, Pleinlaan 2, 1050, Brussels, Belgium
³ Institut für Theoretische Physik, Universität Heidelberg, Philosophenweg 16, 69120, Heidelberg, Germany

kentarou.mawatari@vub.ac.be

Received: 26 October 2010
Revised: 21 November 2010
Published online: 6 January 2011

Abstract

Fortran subroutines to calculate helicity amplitudes with massive spin-3/2 particles, such as massive gravitinos, which couple to the standard model and supersymmetric particles via the supercurrent, are added to the HELAS (HELicity Amplitude Subroutines) library. They are coded in such a way that arbitrary amplitudes with external gravitinos can be generated automatically by MadGraph, after slight modifications. All the codes have been tested carefully by making use of the gauge invariance of the helicity amplitudes.