Name: Manuel J. Vicente (email_not_shown)
Date: 11/23/15-04:27:34 PM Z

  using F9.0.0 I get an strange result from FermionSpinSum:

part1 = Spinor[pp, m].(GA[mu] f1 + GA[mu, 5] fa).Spinor[p, m]
part1cc = ComplexConjugate[part1] /. mu -> nu
aux=FermionSpinSum[part1cc part1]

4*f1^2*(Pair[LorentzIndex[mu], Momentum[pp]]*Pair[LorentzIndex[nu], Momentum[p]] +
  Pair[LorentzIndex[mu], Momentum[p]]*Pair[LorentzIndex[nu], Momentum[pp]] +
  Pair[LorentzIndex[mu], LorentzIndex[nu]]*(m^2 - Pair[Momentum[p], Momentum[pp]]))

The result is only a part of the full tensor. In fact, it doesn't depend on fa at all! The correct result can be recovered just by

Tr[(DiracSlash[p] + m).(GA[nu] f1 - GA[5, nu] fa).(DiracSlash[pp] +
     m).(GA[mu] f1 + GA[mu, 5] fa)]

The simpler case with nu=mu also fails.

p.s. it works fine in the 8.2 version

best regards
Manuel J. Vicente

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