I seem to have stumbled across a bug in FeynArts output. In feynarts.m there is a line setting the gauge parameter for Goldstone bosons:
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WriteString[outputfile,"GaugeXi[S["<>ToString[FeynArtsNr[PART[S][[i,1]]]]<>",1]] = GaugeXi["<>ToString[Select[GoldstoneBosons[InitalizedVertexCalculaton],(FreeQ[#,PART[S][[i,1]]]==False)&][[1,1]]] <>"] /; a > 1 \n"];
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/; a>1 Also, the lines that do use "/; a>1" should have the "=" sign replaced with ":=", as the output is otherwise faulty and causes problems.
Having said that, I began wondering whether it is always the case that "/;a>1" ? I think in the model files one can set the Goldstone boson to be any component of some multiplet, so maybe the condition should read "/; a=!= GoldstoneIndex" instead?
Regards,
Simonas