I´m trying to calculate the matrix element for a ff->ff mediated by a scalar field. The matrix looks like:
Ma = 1/(SP[k1 - p1] - m^2) Spinor[k1, m1].Spinor[-p1, m1].Spinor[-p2, m].Spinor[k2, m]
But when I request the contract as,
Ma2 = FermionSpinSum[Ma*MaC] // Contract
it does not work, saying "DiracSimplify::spinorsleft: Error! After applying FermionSpinSum to all spinor chains the output
still contains spinors. Evaluation aborted."
What I´m doing wrong? Thanks in advance!
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