MadGraph5_aMC@NLO

Baseline questions about heavy neutral lepton model

Asked by Maksym Ovchynnikov

I have found the following model of heavy neutral lepton:
https://feynrules.irmp.ucl.ac.be/wiki/HeavyN

Using the model, I tried to simulate the process

generate p p > w+, w+ > n1 mu+, (n1 > mu+ mu- vm)

for the case of the mixing of n1 with nu_mu and the mass mn1 = 10 GeV. However, I obtained the following warning:

"Decay without corresponding particle in core process found.
Decay information for particle(s) n1 is discarded.
Please check your process definition carefully.
This warning usually means that you forgot parentheses in presence of subdecay.
Example of correct syntax: p p > t t~, ( t > w+ b, w+ > l+ vl)"

I do not understand what is a reason for this warning. Could you please clarify it to me?

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

Well you use a wrong syntax, the code realises that you are likely doing something wrong and raise that error.

I guess that what you want to do is
generate p p > w+, (w+ > n1 mu+, n1 > mu+ mu- vm)

The reason of such paranthesis is the following one if you have the following process
generate p p > h z , h > z e+ e-, z > mu+ mu-

It is ambiguous which z you want to decay. With the syntax above, we will decay the z from the production
while
generate p p > h z , (h > z e+ e-, z > mu+ mu-)
will decay the Z coming from the Higgs decay

Cheers,

Olivier

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