Name: Vladyslav Shtabovenko 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.