Name: Maksym Date: 02/04/18-01:43:56 PM Z
Hi!
I’m trying to evaluate some squared amplitude. My code looks as follows:
{ScalarProduct[p3, p3] = m\[Chi]^2,
ScalarProduct[p1, p1] = m\[Chi]^2,
ScalarProduct[p2, p2] = mp^2, ScalarProduct[p4, p4] =
mp^2,
ScalarProduct[p1, p2] =
Sqrt[p^2 + m\[Chi]^2] Sqrt[p^2 + mp^2] + p^2
,
ScalarProduct[p1, p3] =
Sqrt[p^2 + m\[Chi]^2] Sqrt[q^2 +
m\[Chi]^2] - p*q*Cos[\[Theta]],
ScalarProduct[p1, p4] =
Sqrt[p^2 + m\[Chi]^2] Sqrt[q^2 + mp^2] +
p*q*Cos[\[Theta]],
ScalarProduct[p2, p3] =
Sqrt[p^2 + mp^2] Sqrt[q^2 + m\[Chi]^2] +
p*q*Cos[\[Theta]],
ScalarProduct[p2, p4] =
Sqrt[p^2 + mp^2] Sqrt[q^2 + mp^2] -
p*q*Cos[\[Theta]],
ScalarProduct[p3, p4] =
Sqrt[q^2 + m\[Chi]^2] Sqrt[q^2 + mp^2] +
q^2};
Print[“Amplitude:”]
amplitude =
1/(ScalarProduct[p1 - p3, p1 - p3] -
m\[Phi]^2)
g\[Phi]\[Chi]\[Chi] yN
Sin[\[Alpha]] SpinorUBar[p4,
mp].SpinorU[p2,
mp] SpinorUBar[p3, m\[Chi]].SpinorU[p1,
m\[Chi]]/(1 -
ScalarProduct[p1 - p3, p1 - p3]/pel^2)^2 // Contract //
Simplify
amplitudec = ComplexConjugate[amplitude];
Print[“Squared amplitude:”]
fermionsummedamplitude[p_, q_, m\[Chi]_, mp_,
g\[Phi]\[Chi]\[Chi]_,
yN_, \[Alpha]_, pel_] =
FermionSpinSum[amplitude amplitudec] /. DiracTrace -> TR //
Contract // Simplify
However, the scalar products aren’t substituted in the denominator of expression (although they’re substituted in the numerator), so the output looks like
…/((p1-p3)^2 - mphi^2)^2(pel^2 - (p1-p3)^2)^4.
Could you please tell me what is the reason for this and how to force FeynCalc to substitute the scalar products in the denominator?