Name: V. Shtabovenko (email_not_shown)
Date: 09/20/18-04:17:26 PM Z


Hi,

if there are no Dirac traces, or the number of g^5 matrices in each trace
is even, you can also use the conventional dimension regularization
(CDR). However,
you must ensure that your input expression is purely D-dimensional,
including
spinors and polarization vectors. In CDR everything is evaluated in
D-dimensions
and there are no 4-dimensional quantities, until you evaluate all the
integrals and
take the limit D->4.

This is why FeynCalc does not allow you to mix D and 4 dimensional
objects unless you are using the BMHV scheme. Even expressions like

DiracSimplify[GA[i].GSD[p].GA[i]]

will lead to errors, since in CDR it must be

DiracSimplify[GAD[i].GSD[p].GAD[i]]

There is a good reason for that, since in the past people often were
sloppy with the dimensions and then complained about wrong results.

I suppose that in your input expression there are some 4-dimensional
objects that lead to this error. If you correct that, the error message
should disappear.

Cheers,
Vladyslav

Am 18.09.18 um 23:08 schrieb Yasemin:
> Hello,
>
> I have problems calculating of rho-pion-nucleon triangle loop diagram
> in FeynCalc. An error message appears like "Error! DiracTrick has
> encountered a fatal problem and must abort the computation. The
> problem reads: Incorrect combination of dimensions and g^5 scheme!
>>> ". I believe it is because of the problem with dimensional
> regularisation of Levi-Civita and gamma5. I have read the previous
> writings related with this issue. In the case of using BMHV scheme
> calculation of counter terms was recommended for an amplitude
> including trace of gamma matrices. In the amplitude that I try to
> calculate there is no trace actually. Is that mean I can use BMHV
> scheme without calculation of some counter terms separately?
>
> I may have asked an unreasonable question. Are there any other
> suggestions to solve the problem?
>
> Thank you very much for the support in advance!
>



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