MadGraph5_aMC@NLO

Calculate cross section times relative velocity

Asked by Zhao-Huan Yu

Hi,

I would like to calculate the dark matter annihilation cross section times relative velocity, sigma*|v_1-v_2|, in the zero velocity limit. However, since the definition of cross section involves a factor of 1/|v_1-v_2|, the MadGraph calculation for sigma blows up in this limit. I'm trying to remove this factor from the source code, but I haven't find it. Can you tell me which source file takes this factor into account?

Best regards,
Zhao-Huan

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
Mihailo Backovic Edit question
Solved by:
Zhao-Huan Yu
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Mihailo Backovic (mbackovic) said : 		#1

Hi Zhao-Huan,

Could you provide more information about your calculation. Namely, what is the particular process you are trying to simulate?
Do you need a particular annihilation channel, or total?

Best,

Mihailo

Revision history for this message
Zhao-Huan Yu (yzhxxzxy) said : 		#2

Hi Mihailo,

I need to simulate a particular annihilation channel, for instance, chi chi > w+ w-. After generating this channel in MadGraph, I output it into a directory. Then I try to modify the source code in this directory.

Best,
Zhao-Huan

Revision history for this message
Zhao-Huan Yu (yzhxxzxy) said : 		#3

I think I've found the related source file. It is SubProcesses/genps.f. The 1/|v_1-v_2| factor is involved through the 'flux' variable in the 'gen_mom' subroutine.