MadGraph5_aMC@NLO

Compute two points vertex

Asked by Nicolas Crépet

Dear MG5 experts,
I'm working on BSM simulation with MG5 and a custom UFO model of dark photon. I'm trying to compute the production of dark photon in an upc like this diagram:
https://cernbox.cern.ch/s/Oev6DnGVtSSnCrH
Where \epsilon is a custom effective vertex that transform a photon into a darkphoton.

I can't generate diagram like this one. One told me that is because MG5 can't handle two points interactions, and show me this old version of Madgraph ( https://code.launchpad.net/~maddevelopers/mg5amcnlo/two_point_interactions) , but I don't understand how to use it. Is there any plan on implement this kind of things in the last version of MG5 ?

Thank for your help,
Nicolas

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Olivier Mattelaer
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Best Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi Nicolas,

Indeed, I do not think that any official version of MG5aMC does support two point interactions.
They were indeed the attempt that you point to, but this was an attempt based on version 0.5 of the code (in 2010).
So this is certainly not something I would advise to use since this is even before the first official release, so we have no way to know the exact status of the code for that version.

For example, I do not see any Template directory, so my guess is that version was still requiring a working version of MG4 to provide the template to generate the code. Since MG4 was using f77 compiler, you are good to
1) change all the makefile to make change f77 by gfortran (super simple obviously)
2) debug more than 10 years of update of syntax of gcc (which is a waste of your time).

When I discuss this with Hua-Sheng (which I guess point you to that code), I was using that to show what would be needed to implement such feature. Not as a code to use.

My suggestion here would be to check alternative to 2 point interaction:
1) by changing the propagator of the photon/dark-photon
2) by adding a fake particle that would transform the 2 point interaction into a three point interaction (without changing the amplitude obviously). This is obviously kind of a hack but might be simple to do.

Cheers,

Olivier

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Nicolas Crépet (ncrepet) said : 		#2

Thanks Olivier Mattelaer, that solved my question.

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Nicolas Crépet (ncrepet) said : 		#3

Thanks for your answer, I will look into that.