Name: Vladyslav Shtabovenko (email_not_shown)
Date: 07/26/17-04:45:11 PM Z


Am 25.07.2017 um 10:56 schrieb Vladimir:
> I need to calculate the amplitude which has two GA[5] matrices wrapped by DiracTrace.
> I also use, as I suppose, prescriptions to take limit D->4. But in the final result I have an expression which depends on D.
>
> The code is following:
>
> << FeynCalc`;
> $LimitTo4 = True;
> $LimitTo4IRUnsafe = True;
>
> $Larin = True;
> $West = False;
> $BreitMaison = False;
>
> DiracTrace[(ME - GSD[q]).(gr GSD[p1].GA[6] + gl GSD[p1].GA[7]).(ME+GSD[k - q]).(gr GSD[p2].GA[6] + gl GSD[p2].GA[7])] FAD[{q,ME}, {-k + q, ME}] // FCI //TID[#,q,ToPaVe->True,UsePaVeBasis->True] & // Contract
>
> Is there exist built-in mechanism which provides output that does not depend on D? Or I need to take this limit with help of my own procedures?
>

No, FeynCalc does not take the limit D->4 automatically. That would also
be very dangerous, since the loop integrals in the final expression
might contain all kinds of UV and IR divergences and doing something
like /.{D->4} would inevitably lead to the wrong finite part.



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