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I am trying to implement operators of the form $$ \bar{q}_L \gamma^\mu T^A q_L \bar{q}_L \gamma_\mu T^A q_L $$ where T^A are the SU(3) generators and $q_L$ is the Electroweak SU(2) doublet.

I use the same .fr file of the Standard model, i.e. SM.fr, where I added the following operators

L81qq:=C81qq/Lambda^2 Module[{ii,jj,kk,kk1,jj1,mu,aa,cc,sp1,sp2,sp3,sp4,cc1,cc2,cc3},  (QLbar[sp1,jj,1,cc].QL[sp2,jj,1,cc2] Ga[mu,sp1,sp2]) T[aa,cc,cc2]T[aa,cc3,cc4](QLbar[sp3,jj1,1,cc3].QL[sp4,jj1,1,cc4] Ga[mu,sp3,sp4])];

where the parameters are defined as

 Lambda== {
        ParameterType -> External,
        ParameterName -> Lambda,
        BlockName -> DIM6,
      InteractionOrder -> {NP,-1},
        Value -> 1000,
      TeX -> \[CapitalLambda],
        Description -> "Scale of the new physics"}

and

C81qq== {
        ParameterType -> External,
        ParameterName -> C81qq,
        BlockName -> FourFermion,
        Value -> 1,
      TeX -> Subsuperscript[C,qq,"(8,1)"],
        Description -> "coefficient of O81qq"},

Feynrules manages to reproduce the feynman rules of this 4-fermion operator and also the FeynArts output. But, when I try to draw the diagrams via

 << HighEnergyPhysics`FeynCalc`;

Loading FeynCalc from /home/user/.Mathematica/Applications/HighEnergyPhysics

FeynCalc 8.2.0 For help, type ?FeynCalc, open FeynCalcRef8.nb or visit www.feyncalc.org

FeynArts 3.9 patched for use with FeynCalc

top = CreateTopologies[0, 2 -> 2]; 

diags = 
 InsertFields[top, {F[3, {1}], F[3, {1}]} -> {F[3, {1}], F[3, {1}]}, 
  InsertionLevel -> {Classes}, Model -> "Standard_Model_dijets_FA", 
  GenericModel -> "Standard_Model_dijets_FA", 
  ExcludeParticles -> {V[1], V[2], V[3], S[1], V[4], 
    S[2]}];

I get the error

loading generic model file /home/user/.Mathematica/Applications/HighEnergyPhysics/FeynArts/Models/Standard_Model_dijets_FA.gen

TagSetDelayed::tagnf: Tag FourVector not found in -mom_^mu_. >>

Pattern::patvar: First element in pattern Pattern[b_,_] is not a valid pattern name. >>

What is the problem?

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  • $\begingroup$ Can you format the code like you did here: mathematica.stackexchange.com/questions/59527/…? $\endgroup$
    – QuantumDot
    Jul 1, 2016 at 12:23
  • $\begingroup$ Is there a reason C81qq and Lamdba are followed by == instead of a single =? $\endgroup$
    – Feyre
    Jul 1, 2016 at 12:24
  • $\begingroup$ This is the standard format of Feynrules, I.e. defining new parameters with == $\endgroup$
    – apt45
    Jul 1, 2016 at 12:43

2 Answers 2

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First of all you need to update to FeynCalc 9, FC 8.2 is already outdated. Please use the development version:

https://github.com/FeynCalc/feyncalc/wiki/Installation#dev_automatic_installation

I'm not using FeynRules myself, but I have already been asked to make FeynCalc compatible with FeynRules+FeynArts and according to the user who needed this, everything worked at the end. So please have a look at this message and the subsequent replies

http://www.feyncalc.org/forum/1034.html

If there are still issues left, you can write to the mailing list or directly to me, so we will find a solution.

Cheers,

Vladyslav

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  • $\begingroup$ Thanks Vladyslav, I will write to the mailing list because I have still problems. $\endgroup$
    – apt45
    Jul 1, 2016 at 21:49
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You need to patch the model for use in FeynCalc:

$LoadFeynArts=True;
<<FeynCalc`;
FAPatch[PatchModelsOnly -> True]
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  • $\begingroup$ Until not so long time ago it wouldn't have worked even with patching, since FeynCalc couldn't work out the relative signs between diagrams with 4-fermion vertices. But since Issue #46 was resolved, it indeed works out of the box, as one would expect it. Dev version is required, though. $\endgroup$
    – vsht
    Jan 2, 2020 at 0:17

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