Hi,
add
// PropagatorDenominatorExplicit // ExpandScalarProduct
to rewrite the FeynAmpDenominator as a polynomial in scalar products.
Apart from that, there are built-in functions for writing spinor chains
(SpinorU, SpinoUBar,
SpinorV, SpinorVBar) and introducing Mandelstam variables
(SetMandelstam). Just look at the supplied examples.
Cheers,
Vladyslav
Am 12.10.18 um 04:25 schrieb Daniel:
> 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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