**Next message:**Matt Rizik: "Is there a method in FeynCalc for collecting like powers of four vectors? rizikmat@msu.edu"**Previous message:**Marco V: "Fail to TID completely vitti.marco15@gmail.com"**In reply to:**Marco V: "Fail to TID completely vitti.marco15@gmail.com"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]**Mail actions:**[ respond to this message ] [ mail a new topic ]

Hi,

just add the option ToPaVe->True to TID.

MBOX = ChangeDimension[(1/(16 Pi^4)) TID[integrandBOX, k,

UsePaVeBasis -> True, ToPaVe -> True], 4] // Simplify

that's all. ToPaVe is also a separate function

?ToPaVe

ToPaVe[expr,q] converts all the scalar 1-loop integrals that depend on

the momentum q to scalar Passarino Veltman functions A0, B0, C0, D0 etc.

Cheers,

Vladyslav

Am 19.04.2018 um 06:54 schrieb Marco V:

*> Hello,
*

*>
*

*> I am using FeynCalc 9.2.0 and I am trying to compute the amplitude for a box diagram in QED, but when I use TID to decompose the loop integral, it seems that FC does not convert a denominator into a PaVe scalar function.
*

*>
*

*> Setting the integrand
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*>
*

*> numBOX = e^4 (SpinorUBarD[q1,
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*> m\[Mu]].GAD[\[Alpha]].(GSD[p1 - k] +
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*> m\[Mu]).GAD[\[Beta]].SpinorUD[p1, m\[Mu]] SpinorUBarD[q2,
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*> me].GAD[\[Alpha]].(GSD[k + p2] + me).GAD[\[Beta]].SpinorUD[p2,
*

*> me]);
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*>
*

*> integrandBOX =
*

*> numBOX*FAD[{p1 - k, m\[Mu]}, {k + p2, me}, {k + p2 - q2,
*

*> SmallVariable[\[Lambda]]}, {k, SmallVariable[\[Lambda]]}];
*

*>
*

*>
*

*> and putting it in TID
*

*>
*

*> MBOX = ChangeDimension[(1/(16 Pi^4)) TID[integrandBOX, k,
*

*> UsePaVeBasis -> True], 4] // Simplify
*

*>
*

*>
*

*> the result I obtain is mostly in terms of D coefficient functions and independent from the loop momentum k (as I expect), but there is also a term
*

*>
*

*> -2 (me^2 + m\[Mu]^2 - s) Spinor[Momentum[q1], m\[Mu],
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*> 1].GA[\[Alpha]].Spinor[Momentum[p1], m\[Mu], 1] Spinor[
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*> Momentum[q2], me, 1].GA[\[Alpha]].Spinor[Momentum[p2], me,
*

*> 1] FAD[{k, SmallVariable[\[Lambda]]}, {k + p1, m\[Mu]}, {k - p2,
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*> me}, {k - p2 + q2, SmallVariable[\[Lambda]]}, Dimension -> 4]
*

*>
*

*> which I understand should correspond to a D0 but it is not transformed in it.
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*>
*

*> If I try to use TID on the last expression, it remains unchanged.
*

*> If instead I use OneLoop it gives me exactly the D0 which I was looking for.
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*>
*

*> I suppose the problem is related to the choice of dimension, but I don't understand why the rest of the result is correctly in terms of PaVes. Can you explain what I am doing wrong?
*

*>
*

*> Many Thanks
*

*>
*

**Next message:**Matt Rizik: "Is there a method in FeynCalc for collecting like powers of four vectors? rizikmat@msu.edu"**Previous message:**Marco V: "Fail to TID completely vitti.marco15@gmail.com"**In reply to:**Marco V: "Fail to TID completely vitti.marco15@gmail.com"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]**Mail actions:**[ respond to this message ] [ mail a new topic ]

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