Name: Luca Marzola (email_not_shown)
Date: 11/14/17-03:38:01 PM Z


Hello guys,

I have been trying to use FeynArts and FeynCalc to compute the electron g-2 in QED, similarly to the example you provide. When I invoke OneLoop I obtain the following error

DiracTrick::failmsg: Error! DiracTrick has encountered a fatal problem and must abort the computation. The problem reads: Incorrect combination of dimensions and g^5 scheme!

I read the question already asked by Maksym in the mailing list on the 07/24/17, but still I cannot understand what is going on. Essentially I am feeding OneLoop with the amplitude straight from FCFAConvert[]:

$LoadFeynArts = True;
<< FeynCalc`;

SetOptions[{Plot, ParametricPlot, LogPlot, LogLogPlot},
  BaseStyle -> FontSize -> 12, LabelStyle -> Black, Frame -> True,
  Axes -> None, FrameTicksStyle -> Black, AspectRatio -> 2/3,
  ImageSize -> 400, PlotStyle -> Thick];
SetDirectory[NotebookDirectory[]];

(*FaynArts verbosity *)
$FAVerbose = 0;

proc0 = {-F[1, {1}], F[1, {1}]} -> {V[1]};
(*F[1,{1}] is the electron*)

top1 = CreateTopologies[1, 2 -> 1,
   ExcludeTopologies -> {Tadpoles, WFCorrections}];

ins1 = InsertFields[top1, proc0, ExcludeParticles -> {},
   InsertionLevel -> {Classes}, GenericModel -> "Lorentz",
   Model -> "QED"];

Paint[ins1, ColumnsXRows -> {1, 1}, Numbering -> None,
  SheetHeader -> None];

amp1 = FCFAConvert[
   CreateFeynAmp[ins1, Truncated -> True,
    PreFactor -> -(2 \[Pi])^-4], ChangeDimension -> D,
   UndoChiralSplittings -> True, IncomingMomenta -> {-p2, p1},
   OutgoingMomenta -> {-p2 + p1}, LoopMomenta -> {-k}, List -> False,
   SMP -> True,
   FinalSubstitutions -> {SMP["m_e"] -> m, SMP["e"] -> e }];

OneLoop[k, amp1, OneLoopSimplify -> True]

>>DiracTrick::failmsg: Error! DiracTrick has encountered a fatal problem and must abort the computation. The problem reads: Incorrect combination of dimensions and g^5 scheme!

What am I doing wrong? Iím on Mathematica 11.2.0.0, macOS high sierra, and latest installation of FeynCalc and FeynArts (installed and patched by FeynCalc with your automatic installation method).

Thank you for your help and kind regards,
L.



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