Name: Vladyslav Shtabovenko (email_not_shown)
Date: 05/03/16-10:35:19 AM Z


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


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


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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