I'm evaluating a 2-to-3 cross-section. The matrix element takes the form
f = 1/(ScalarProduct[k1 + k2, k1 + k2] - mp^2) PolarizationVector[
k2, \[Mu]] SpinorUBar[p1,
mp].GA[\[Nu]].(vf - af GA5).(GS[k1 + k2] + mp).GA[\[Mu]].SpinorU[
k1, mp] SpinorUBar[p3, m].GA[\[Nu]].(1 - GA5).SpinorV[p2, 0]
After a lot of integrations I obtain negative result for the cross-section. However, if I change GS[k1 + k2] + mp to GS[k1 + k2] - mp, the result is positive.
Could you please clarify this point? Maybe there is internal convention about signs inside the fermion propagator, according to metric sign convention and other, or something like that?
P.S. I've checked all other steps of the calculation.
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