FeynCalc amplitude squared giving polarisation vector with external momentum as its indices.

[scsa007316]

I calculated the amplitude for a process using feynarts and feyncalc. And in the squared amplitude expression it is giving terms which have polarisation vectors with external momentum as its indices. Now I know this result does not make sense something went wrong somewhere.
Here is what I did, I calculated the amplitude using " amp[0] =
FCFAConvert[CreateFeynAmp[if1], IncomingMomenta -> {p1, p2},
OutgoingMomenta -> {k1, k2, k3, k4}, UndoChiralSplittings -> True,
ChangeDimension -> 4, List -> False, SMP -> True, Contract -> True]"
and stored it in amp[0], this result was good it made sense. Then I computed squared amplitude using - " ampSquared[0] =
Simplify[
DiracSimplify[(FermionSpinSum[#1, ExtraFactor -> 1/4] &)[
FeynAmpDenominatorExplicit[amp[0]*camp[0]]]]]" and it gave terms like Overscript[[Epsilon], _]^(Overscript[k1, _]Overscript[k2, _]Overscript[k4, _]Overscript[p1, _]) (Overscript[k1, _][CenterDot]Overscript[p2, _]) (Overscript[k1, _][CenterDot]Overscript[k3, _]).

The process considered is 2 to 4 process. Any help/suggestions?

[vsht]

My suggestion would be to read the docu first, especially the tutorial part that explains the notation <https://feyncalc.github.io/FeynCalcBookDev/InternalExternal.html> Am 25. Oktober 2023 08:14:59 UTC schrieb Aadarsh singh ***@***.***>:

…

I calculated the amplitude for a process using feynarts and feyncalc. And in the squared amplitude expression it is giving terms which have polarisation vectors with external momentum as its indices. Now I know this result does not make sense something went wrong somewhere. Here is what I did, I calculated the amplitude using " amp[0] = FCFAConvert[CreateFeynAmp[if1], IncomingMomenta -> {p1, p2}, OutgoingMomenta -> {k1, k2, k3, k4}, UndoChiralSplittings -> True, ChangeDimension -> 4, List -> False, SMP -> True, Contract -> True]" and stored it in amp[0], this result was good it made sense. Then I computed squared amplitude using - " ampSquared[0] = Simplify[ DiracSimplify[(FermionSpinSum[#1, ExtraFactor -> 1/4] &)[ FeynAmpDenominatorExplicit[amp[0]*camp[0]]]]]" and it gave terms like Overscript[\[Epsilon], _]^(Overscript[k1, _]Overscript[k2, _]Overscript[k4, _]Overscript[p1, _]) (Overscript[k1, _]\[CenterDot]Overscript[p2, _]) (Overscript[k1, _]\[CenterDot]Overscript[k3, _]). The process considered is 2 to 4 process. Any help/suggestions? -- Reply to this email directly or view it on GitHub: #236 You are receiving this because you are subscribed to this thread. Message ID: ***@***.***>

[scsa007316]

That was straight to the point suggestion. Thanks.

[scsa007316]

Query Resolved. It was my bad.