Name: Daniel (email_not_shown)
Date: 10/11/18-10:25:26 PM Z

Hey guys,

Sorry for the naive question. I want to get the matrix expression just in terms of the Mandelstam variables, but seems like I have missed something, here the example and the end the output:

ScalarProduct[p1, p1] = m1^2;
ScalarProduct[k1, k1] = m1^2;
ScalarProduct[p2, p2] = m^2;
ScalarProduct[k2, k2] = m^2;
ScalarProduct[p1, p2] = (s^2 - m^2 - m1^2)/2;
ScalarProduct[k1, p1] = -((t^2 - 2 m1^2)/2);
ScalarProduct[p2, k1] = -((u^2 - m^2 - m1^2)/2);

Ma = (yx*yf)/(SP[k1 - p1] - m^2)
Spinor[k1, m1].Spinor[p1, m1] Spinor[k2, m].Spinor[p2, m]

MaC = ComplexConjugate[Ma]

Ma2 = FermionSpinSum[Ma*MaC] // Contract

1/4 Ma2 /. DiracTrace -> Tr /. k2 -> -k1 + p1 + p2 /.
u -> 2 m1^2 + 2 m^2 - t - s // Simplify

>> The output still contains the 4-momenta vectors:

(2 yf^2 yx^2 (2 m1-t) (2 m1+t) (Overscript[p2, _]\[CenterDot](-Overscript[k1, _]+Overscript[p1, _]+Overscript[p2, _])+m^2))/(m^2-((Overscript[k1, _]-Overscript[p1, _]))^2)^2

what I´m missing in order to have it just in terms of s, t and de masses?

Thanks
&
Cheers,

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