Name: Pedro Ruiz-Femenia (email_not_shown)
Date: 02/01/17-04:02:10 PM Z


Hi Vladyslav,

I seem to get a different result for a trace with an even number of gamma5's using Larin's prescription ($Larin = True) as compared to the naive anticommuting scheme: (I am using FeynCalc 9.2.0)

In[1]:= trace:=Tr[GAD[mu].DiracMatrix[5].GAD[mu].DiracMatrix[5]]

In[2]:=
$Larin = False;
trace
Out[2]:= -4D

In[3]:=
$Larin = True;
trace
Out[3]:= -(2/3) (D-3) (D-2) (D-1) D

The results differ for D!=4. The reason may be that with the Larin's prescription implemented in FeynCalc, GAD[mu].DiracMatrix[5] at the end of the trace is first replaced by the LeviCivita tensor with three gamma's, and the resulting trace with the remaining gamma5 gives another LeviCivita. Then the contraction of the two tensors is done treating them as D-dimensional. This gives something different to what you will get putting gamma5's together in the first place.

I can of course avoid the problem by separating traces with odd and even number of gamma5's, and using NDR on the latter. But sometimes (this was my case) one carelessly writes the expression for the full trace, and one expects that terms with even number of gamma5's will be the same no matter which prescription has been set. Is there a way to set Larin's gamma5 scheme in FeynCalc to avoid the issue above?

Thanks for your support of FeynCalc!

Pedro



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