Name: Rakhi (email_not_shown)
Date: 04/14/15-02:20:34 PM Z


Hi, I'm computing a spin sum and propagator contraction with FeynCalc 8.2.0 and the results of the contraction don't agree with what I expect (also disagrees with computation by hand).

Code to get spin sum
====================================
ClearScalarProducts
ScalarProduct[q, q] = M^2; ScalarProduct[k1, k1] = m1^2;
ScalarProduct[k2, k2] = m2^2; ScalarProduct[k3, k3] = m3^2;
ScalarProduct[k2, k3] = 1/2 (M^2 + m1^2 - m2^2 - m3^2 - 2 ScalarProduct[q, k1]);
ScalarProduct[k1, k3] = 1/2 (M^2 - m1^2 + m2^2 - m3^2 - 2 ScalarProduct[q, k2]);
ScalarProduct[k1, k2] = 1/2 (M^2 - m1^2 - m2^2 + m3^2 - 2 ScalarProduct[q, k3]);
ScalarProduct[k3, q] = M^2 - ScalarProduct[q, k2] - ScalarProduct[k1, q];

m2 := 0;

s1 = Spinor[q, M].GA[\[Mu]].(-Ni2 GA[7] + Ni3 GA[6]).Spinor[k1, m1];
s1C = ComplexConjugate[s1] /. {\[Mu] -> \[Rho], Ni3 -> Conjugate[Ni3], Ni2 -> Conjugate[Ni2]};
s2 = Spinor[k2, m2].GA[\[Nu]].GA[7].Spinor[-k3, m3];
s2C = ComplexConjugate[s2] /. {\[Nu] -> \[Sigma]};
Mint = FermionSpinSum[s1 s1C] FermionSpinSum[s2 s2C] /. DiracTrace -> Tr
============================

Then I contract with a massive W propagator:

=============================
prop[\[Mu]_, \[Nu]_, p_, m_] := (MT[\[Mu], \[Nu]] - (FV[p, \[Mu]] FV[p, \[Nu]])/m^2);
Ampsq = Contract[prop[\[Rho], \[Sigma], q - k1, mw].Mint.prop[\[Mu], \[Nu], q - k1, mw]];
=============================

Am I not using the commands correctly, or is there some sort of bug?

Many thanks in advance for your help,
Rakhi



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