The color package takes for its input a combination of group structure constants and generators. If all indices are contracted it will rewrite this input in terms of group invariants in a group and representation independent way.
The whole is based on the paper:
T. van Ritbergen, A.N. Schellekens and J.A.M. Vermaseren: "Group theory factors for Feynman diagrams", Int. J. Mod. Phys. vol. 14 (1999) 41.
The various files are:
| color.h | The library file with the FORM code. Please put this file in a location that is covered by your FORMPATH environment variable. |
| color.tar.gz | Some FORM programs that use color.h. These are simple examples. |
| color.ps | The postscript version of the paper. |
| color.pdf | The pdf version of the paper. |
Known problem: There seems to be a problem with E6 when there are at least
14 vertices. It doesn't seem to check with the Cvitanovic algorithm. The
origin can be either in the checking programs, the paper, color.h or the
Cvitanovic paper. One of us spent quite some time on this (JV). It didn't
become clear and at the time we didn't have more time to pursue this. For
all other groups everything checked up to 16 vertices.