Name: L.X. Xu (email_not_shown)
Date: 11/03/14-06:06:55 AM Z

hi,
the result of (quark,quarkbar->quark,quarkbar) obtained by FeynCalc is not correct, one term of the result differ by a minus sign from the correct. We can just find the correct at page 196 of Langacker's book<the standard model and beyond> or page 571 of Peskin EQ(17,70).
is there an problem of my code or a bug?

I'm appreciate the help!
Here is my code:
Quit;
<< HighEnergyPhysics`FeynCalc`

ClearScalarProducts;
{ScalarProduct[p1, p1] =
ScalarProduct[p2, p2] =
ScalarProduct[p3, p3] = ScalarProduct[p4, p4] = 0,
ScalarProduct[p1, p2] = ScalarProduct[p3, p4] = s/2,
ScalarProduct[p1, p3] = ScalarProduct[p2, p4] = -t/2,
ScalarProduct[p1, p4] = ScalarProduct[p2, p3] = -u/2
};
ScPr[p_, m_] := -I/(ScalarProduct[p] - m^2) // ExpandScalarProduct;
ftrace = {DiracTrace -> Tr2, D -> 4};
SUNN = 3;
SetOptions[SUNSimplify, SUNNToCACF -> False];
qav = 6;

f1 = SpinorVBar[p2, 0].QGV[\[Alpha], k].SpinorU[p1, 0] ScPr[p1 + p2,
0] SpinorUBar[p3, 0].QGV[\[Alpha], k].SpinorV[p4, 0] // Explicit;
f2 = SpinorUBar[p3, 0].QGV[\[Alpha], k].SpinorU[p1, 0] ScPr[p1 - p3,
0] SpinorVBar[p2, 0].QGV[\[Alpha], k].SpinorV[p4, 0] // Explicit;
f = f1 + f2
f1s = SpinorUBar[p1, 0].QGV[\[Beta], l].SpinorV[p2,
0] (-ScPr[p1 + p2, 0]) SpinorVBar[p4, 0].QGV[\[Beta],
l].SpinorU[p3, 0] // Explicit;
f2s = SpinorUBar[p1, 0].QGV[\[Beta], l].SpinorU[p3,
0] (-ScPr[p1 - p3, 0]) SpinorVBar[p4, 0].QGV[\[Beta],
l].SpinorV[p2, 0] // Explicit;
fstar = f1s + f2s

Msq = FermionSpinSum[
f fstar // Explicit // Expand]/(qav^2 Gstrong^4) /. ftrace //
Contract // Simplify // SUNSimplify // Expand

standard = 4/9 ((s^2 + u^2)/t^2 + (u^2 + t^2)/s^2 - 2/3 u^2/(s t))
TrickMandelstam[Msq - standard, {s, t, u, 0}]

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