**Next message:**Tramontano Francesco: "One Loop Scalar Integrals"**Previous message:**Tramontano Francesco: "FAToFC and Feynman Parametrization"**In reply to:**Tramontano Francesco: "FAToFC and Feynman Parametrization"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]**Mail actions:**[ respond to this message ] [ mail a new topic ]

Hi Francesco.

*>1) I will try the updated version, however, to continue the calculation I
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*>replaced the whole FA-Quark-Gluon-Vertex with the FC QuarkGluonVertex in
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*>this way:
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*>
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*>ampFA = CreateFeynAmp[ff];
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*>ampPL = PickLevel[Classes][ampFA];
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*>ampF1 = ToFA1Conventions[ampPL];
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*>ampF1 /. {((-I)*GStrong*DiracGamma[LorentzIndex[cli_]].DiracGamma[6]*
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*> SUNT[_[_, 1], _, _] -
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*> I*GStrong*DiracGamma[LorentzIndex[cli_]].DiracGamma[7]*
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*> SUNT[_[_, 1], _, _]) ->
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*> QuarkGluonVertex[cli,
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*> a], ((-I)*GStrong*DiracGamma[LorentzIndex[cli_]].DiracGamma[6]*
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*> SUNT[_[_, 2], _, _] -
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*> I*GStrong*DiracGamma[LorentzIndex[cli_]].DiracGamma[7]*
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*> SUNT[_[_, 2], _, _]) ->
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*> QuarkGluonVertex[cli,
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*> b],
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*> DiracSpinor[mom_, mas_] -> Spinor[mom, mas], SumOver[_[_, _], _] ->
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*>1,
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*> SumOver[_[_, _], _, _] -> 1,
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*> GStrong -> Gstrong, Index[Gluon, 1] -> "a", Index[Gluon, 2] -> "b"};
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*>
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*>and used the FC SUN machinary. Is there any problem in doing so?
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No, on the contrary, nice that you found a way around the "bug" in my

previous update (I had forgotten that Rolf actually already put

QuarkGluonVertex in FeynCalc) The newest update should however work nicely

as illustrated by the notebook attached to my previous post

http://www.feyncalc.org/forum/0097.html

W.r.t. Gstrong it's just a typo of mine. In the original FeynArts model

file "SMQCD.mod" the symbol GS is used; but this symbol is already in use

by FeynCalc, so FAPatch changes it to GStrong; I've changed that to Gstrong

now (not that it's all that important).

*>2) In the updated version too it seems that there is a problem in FAToFC
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*>when a vector boson is in the initial state: renaming momenta some
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*>particle in FA notation became antipaticle in FC notation
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*>
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*>I tried with:
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*>
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*>tt = CreateTopologies[0, 2 -> 1];
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*>aa = InsertFields[tt, {V[3], F[3, {1}]} -> {F[4, {1}]},
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*> InsertionLevel -> Classes, Model -> "SMQCD", GenericModel ->
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*>"Lorentz"];
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*>
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*>after FAToFC d-quark momentum K1 become -p3. (different momentum
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*>conservation conventions?)
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Notice that what you see as k1 (with "Default Output Format Type" set to

"TraditionalForm" - done automatically on loading FeynCalc) is actually

FourMomentum[Outgoing, 1] (try FourMomentum[Outgoing, 1] // StandardForm).

That is, FeynArts keeps track of which particles are incoming and which are

outgoing. FeynCalc simply counts all particles as incoming. Therefore the

change of sign.

*>3) In performing integration over loop momenta I don't succeded to use
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*>FeynmanParametrize1, FeynmanReduce and FeynmanDoIntegrals, maibe I was
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*>inserting wrong input. Could you write an example? Is there some package
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*>with evaluated scalar function integrals in FC or elsewhere?
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Hmm. So you tried out FeynmanParametrize1, FeynmanReduce and

FeynmanDoIntegrals... I added these functions some time ago and wanted to

develop them further, never had the time and didn't do much testing either.

They are really to be considered experimental at best. As long as you are

at one loop, why don't you just use OneLoop and get your amplitude in terms

of standard Passarino-Veltman functions? OneLoop is heavily tested by

both Rolf and myself.

I attach a notebook (an unfinished calculation) to show you in which

direction I was going with FeynmanParametrize1, FeynmanReduce and

FeynmanDoIntegrals. Notice that, as always, you can get information about

what's happening by setting $VeryVerbose to 1,2 or 3 instead of 0. Bug

reports, bug fixes and improvements are of course very welcome.

Frederik

- text/plain attachment: TwoLoopVacPol-F.nb

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