MadGraph5_aMC@NLO

implementing rare decay in madgraph

Asked by Saurabh Niyogi

Hello Experts,

 I am not sure if my question is related to MG5 or FeynRules team !

 I am trying to implement some rare decays in Madgraph. I found in launchpad where it seems people have done at the UFO level. But it would helpful if it can be done in a simpler way, just like, Pythia can read SHLA file where BRs of required process can be directly fed by hand. Can it be done in MG5 ? If not, how can we implement such rare decays (which includes mesonic process) in FR ?

Thanks,

Saurabh Niyogi

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

>But it would helpful if it can be done in a simpler way, just like, Pythia can read SHLA file where BRs of required process can be directly fed by hand. Can it be done in MG5 ?

No it can not. MadGraph computes amplitudes (square) and for that we need to know what is the lorentz structure associated to the vertex. This is the price to pay to have more accurate prediction than the naive BR method.
Now if that method is good enough for your case, you can generate your events with madgraph and do the decay within pythia.

> If not, how can we implement such rare decays (which includes mesonic process) in FR ?

You have to implement your Lagrangian inside FeynRules and then ask FR to create the UFO model. (I have basically never use FR, so you should contact them for more help)
If you need to include some form-factors, you have some help here on how those can be implemented:
https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/FormFactors

Cheers,

Olivier

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Saurabh Niyogi (saurabh12102003) said : 		#2

Thanks a lot..

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