Name: Vladyslav Shtabovenko (email_not_shown)
Date: 06/13/17-08:18:58 PM Z


Hi,

Am 13.06.2017 um 16:05 schrieb Stefano Colucci:
> Hi again,
>
> and thanks for your prompt answer. Regarding the use of "." : I guess I was mislead by reading in the documentation page for Contract :
>
> " The "." as multiplication operator is not necessary but just convenient for typesetting.”

Well, for commutative quantities the ordering in the product clearly
does not matter, which is what the documentation page is referring to.

For noncommutative quantities one would always use Dot and not Times.
This is one of the basics of Mathematica (i.e. it has nothing to do with
FeynCalc per se), so in the documentation it is assumed that this point
is understood.

>
> Anyways I followed your suggestions but I still get an error message and no result when calling
>
> In[64]:= DiracTrace[AmpF2, DiracTraceEvaluate -> True, West -> True]
>
> During evaluation of In[64]:= DiracTrace::ndranomaly: You are using naive dimensional regularization (NDR), such that in D dimensions gamma^5 anticommutes with all other Dirac matrices. In this scheme (without additional prescriptions) it is not possible to compute traces with an odd number of gamma^5 unambiguously. Evaluation aborted! >>
>
> Out[64]= $Aborted
>
>
> I have tried to set D->4 before or to use the option West-> True, but no luck so far.
>

First of all, I do not seem to be able to reproduce this on the latest
stable version, c.f. attached notebook.

Second, the West option is relevant only when the BMHV scheme is
activated ($BreitMaison=True). As the message tells you, by default
FeynCalc uses NDR.

Third, if you do not care whether D is set to 4 or not, why don't you
calculate everything in 4D from the very beginning. That would be again
faster.

Cheers,
Vladyslav

> Thanks again for your help,
>
> Stefano
>




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