Date: 05/03/16-10:35:19 AM Z

Hi,

first of all, it would be nice to have a minimal working example to
understand what is going on.

Second, the fact that GaugeXi[x] may still appear in you amplitude
despite using

GaugeRules -> {GaugeXi[Z] -> Infinity, GaugeXi[A] -> Infinity,
GaugeXi[W] -> Infinity}

is actually mentioned in the FeynArts manual, p. 44

"Take care that the choices 0 (Landau gauge) and Infinity (unitary
gauge) actually imply a limit which is in general not correctly taken
with the naive GaugeRules substitution. In such a case the gauge
parameters should remain in the amplitude until after simplification,
and then substituted."

What you can do, is generate the same amplitude using unpatched FeynArts
(<<FeynArts`) on a clean kernel and check if the gauge dependence is
still there

FreeQ[amp,GaugeXi]

If yes, then it is the standard behavior of FeynArts that one has to
work around with suitable code.

Cheers,

Am 02.05.2016 um 17:17 schrieb Camila:
> Hi,
>
> I'm using the Feynarts 3.9 with the FeynCalc 9.0 (I also tested with development version) and I'm getting a problem to use the unitary gauge with the FCFAConvert.
>
> I'm using: Model -> {"SM", "UnitarySM"}, GenericModel -> {"Lorentz",
> "UnitaryLorentz"}
>
> and setting the unitary gauge in the following way:
>
> FCFAConvert[
> CreateFeynAmp[dias, Truncated -> False,
> GaugeRules -> {GaugeXi[Z] -> Infinity, GaugeXi[A] -> Infinity,
> GaugeXi[W] -> Infinity}],
> IncomingMomenta -> {p1, p2}, OutgoingMomenta -> {k1, k2},
> UndoChiralSplittings -> True, ChangeDimension -> 4, List -> False]
>
> In the end the amplitude still depends on \xi_Z. I'm doing something wrong or this could be a bug?
>
> Thank you very much!
>

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