Name: Vladyslav Shtabovenko (email_not_shown)
Date: 12/18/14-10:28:33 AM Z


Hi Sam,

the thing is that in FeynCalc all non-commutative objects (like Dirac or
SU(N) matrices) must be separated by a "." simply because in Mathematica
the usual multiplication "a*b===b*a" is commutative while
the "." multiplication is not "a.b=!=b.a".

In your code you enter Dirac matrices without the "." as if the ordering
doesn't matter, so no wonder that the result is ambiguous. With

Tr[DiracMatrix[a]. DiracMatrix[b]. DiracMatrix[c]. DiracMatrix[d]]

and

Tr[DiracMatrix[a]. DiracMatrix[\[Beta]].
   DiracMatrix[c] .DiracMatrix[\[Delta]]]

you get the correct result in both cases.

BTW, you can also use "GA" instead of DiracMatrix
(see <https://github.com/FeynCalc/feyncalc/wiki/FAQ#fci_fce>
for more details) which is much more compact:

Tr[GA[a,b,c,d]]===(Tr[GA[a,\[Beta],c,\[Delta]]]/.{\[Beta]->b,\[Delta]->d})

Cheers,
Vladyslav

On 17/12/14 23:26, Sam wrote:
> I should mention that I am using Mathematica 10.0.2.0 (released very recently) on a Mac OS X 10.10, with FeynCalc 8.2.0 and FeynArts 3.7 patched for use with FeynCalc.
>
> Thanks again,
> Sam
>



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