multiparticles in BSM models
Hello,
we used FeynRules (v2.3.26) to define a new model that represents a Seesaw (type I) mechanism, to which we added some effective interactions at low energies with mesons. The generation of the model is successful and the UFO files of the model seems to contain the correct particles and vertices. However, we are finding a strange behavior when we use it with MadGraph (v 2.6.6) to compute some decay widths for the new particles introduced.
We have introduced 4 neutrino mass eigenstates: a heavy one (n1) and three massless (v1, v2 and v3).
If we define nu = v1 v2 v3 and generate the process n1 > v1 v1~ nu we obtain a decay rate of 2.3*10^-37 GeV
However if we generate the separate processes:
n1 > v1 v1~ v1, n1 > v1 v1~ v2 and n1 > v1 v1~ v3
we obtain 3.7*10-41, 1.8^*10^-41 and 1.8*10^-41 GeV, which does not add up to the first result.
This happens with several different processes involving neutrinos and we have not been able to determine what is causing it. Also, if we generate n1 > nu nu~ nu we obtain 2.6*10^-26 GeV, much larger than all the individual processes we generate.
We have also noticed that when requesting n1 > nu~ nu nu, all the subprocesses that are generated are labeled as n1>v2~ v2 v3 and so on. However, when we request a process without using the nu definition such as n1 > v2 v2~ v3 they are instead labeled as n1>vl~ vl vl. This is the case even though we *never* defined vl (not in the model nor in the MadGraph interface when generating the events). Maybe this has something to do with this issue?
Any info you could provide on this would be very helpful. If you would like to see the UFO files of the model, I can send them to you by email.
Many thanks in advance,
Pilar
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- Olivier Mattelaer
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