hmm, on my machine (Mathematica 11.3, latest FeynCalc 9.2 stable from
the repository) the above code produces the final result without any
traces or Lorentz indices (see attachment).
I think that the last fix that might have something to do with your
issue is from Jun 14, 2017:
So if you don't have that, you should reinstall FeynCalc 9.2 using the
automatic installer and try again.
Am 30.05.2018 um 00:46 schrieb D. Azevedo:
> Hey Vladyslav,
> Thanks for the reply, though the problem persists. I actually tried your solution before but I ran into the same problem.
> after doing:
> res=((M12 // FermionSpinSum) /. DiracTrace -> Tr) // Contract
> I still get a product of traces, because there are still dummy indexes inside them:
> tr(...GA[alpha]...GA[alphalin]..) tr (... GA[alpha]...GA[alphalin]...)
> Everything is multiplying, so there are no "free indexes" M12 is a Lorentz scalar.
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