MadGraph5_aMC@NLO

How to get subroutine of helicity amplitude

Asked by Keping Xie

Hi everyone,

I want to get the helicity amplitude of a process, such as loop-induced "g g > a a [QCD]".
I have looked at the flies generated by MadGraph_aMC@NLO, in both SubProcess and PV0_0_1_**** directories.
I just found several fortran files, such as matrix1.f, loop_matrix.f etc. These codes return amplitude squared summed/avg over colors and helicities.
Is it possible to get the un-squared helicity amplitude?

I want to extract it and encode to other program.

Best regards!
Keping

Question information

Language:
English Edit question
Status:
Answered
For:
MadGraph5_aMC@NLO Edit question
Assignee:
Valentin Hirschi Edit question
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Last reply:
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Valentin Hirschi (valentin-hirschi) said : 		#1

Sorry for the late reply.

The short answer is no, but mostly because it is ambiguous both because the overall phase of all the amplitudes is arbitrary and because you would have to make a choice as to how to factor out the color structure of your amplitude.

It seems likely that whatever you ultimately want to do with amplitudes could be recast in a manner that uses squared amplitudes, since it the end these are the only physical quantities. But without knowing more about your intent, I cannot say more.

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Provide an answer of your own, or ask Keping Xie for more information if necessary.

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