Name: K.J. Healey Date: 02/21/14-01:30:32 PM Z

[quote]
An example I have encountered is the following (e+ e- -> mu+ mu-):
test = SpinorUBar[k2, m2].GA[mu].SpinorV[k1, m2] SpinorU[p1, m1].GA[
    mu].SpinorVBar[p2, m1] FeynAmpDenominator[
   PropagatorDenominator[s]]
ctest = ComplexConjugate[test]
FermionSpinSum[test ctest]
[/quote]

The problem here might come from (im not at a computer with FC) the fact
that you have GA[mu] listed 4 times in the FSS. So when you have

(ub.GA[mu].u).(vb.GA[mu].v)

and take the complex conjugate, it doesnt relabel the indices. I always do something like:

AMP = (SpinorUBar[k2, m2].GA[mu].SpinorV[k1, m2]) (SpinorU[p1, m1].GA[
    mu].SpinorVBar[p2, m1]);

AMPSQ = FermionSpinSum[Calc[AMP.ComplexConjugate[AMP/.{mu-> nu}]]]/.DiracTrace-> Tr

As my standard squared amplitude.

Also I use the “.” a lot, and Calc[A.A*] before the FSS.