Version 14 (modified by florian.bonnet, 9 years ago) (diff)


Type III Seesaw


  • Carla Biggio
    • Institut de Fisica d'Altes Energies (IFAE), Universitat Autonoma de Barcelona (UAB), Spain
    • email: biggio _at_
  • Florian Bonnet
    • INFN-Padova
    • email: florian.bonnet _at_

Model Description

This model describes the minimal realisation of the Type III Seesaw. It is an extension of the SM where a fermionic triplet is add to the matter content. The fermionic triplet is introduced into the form of a heavy Dirac charged lepton tr+/- and a heavy Majorana neutral lepton tr0.


  • "mu->e gamma and tau->l gamma decays in the fermion triplet seesaw", A. Abada, C. Biggio, F. Bonnet, B. Gavela, T. Hambye, Phys. Rev. D78 (2008) 033007.
  • "Implementation of the Type III Seesaw model in FeynRules/MadGraph? and prospect for discovery with LHC data", C. Biggio, F. Bonnet, xxxxx

Model Files

  • For MadGraph/MadEvent and BRIDGE users: this is a modified version of the file, that can be useful when dealing with small mixing angles (the original file sets to zero couplings smaller than 10-5)
  • typeIIIseesaw.nb: this is a Mathematica notebook that loads the model and export it to the MadGraph and CalcHep format.


In order to validate the implementation of the model we have checked several processes:

  • Comparison with the FeynRules generated Standard Model in MadGraph (sm_FR) of SM 2-to-2 processes :
    • l+l- -> ll
    • l+l- -> VV
    • VV -> VV
    • HH -> VV
    • GG -> GG
    • qq~ -> qq~
    • qq~ -> VV
    • qq~ -> GG

  • Comparison with the FeynRules generated Standard Model in MadGraph (sm_FR) of SM particles decay widths and branching ratios calculated with BRIDGE

  • Comparison with previous studies (see Phys.Rev D78 (2008) 033002) of the production cross section of a pair of triplets at the LHC with 14 TeV as center-of-mass energy:
    • pp -> tr+tr- + pp -> tr+/-tr0


We implemented the couplings to Goldstone bosons so the implmentation allows for the use of Feynman gauge. We have checked that the exportation to the CalcHep format is successfull however we did not check the CalcHep output.

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