= Type III Seesaw =
== Authors ==
* Carla Biggio
* Institut de Fisica d'Altes Energies (IFAE), Universitat Autonoma de Barcelona (UAB), Spain
* email: biggio _at_ ifae.es
* Florian Bonnet
* Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Padova, Italy
* email: florian.bonnet _at_ physik.uni-wuerzburg.de
== Model Description ==
This model describes the minimal realisation of the Type III Seesaw. It is an extension of the Standard Model where a fermionic triplet is added to the matter content in order to give mass to one neutrino via a seesaw mechanism. The fermionic triplet is introduced under the form of a heavy Dirac charged lepton tr^+/-^ and a heavy Majorana neutral lepton tr^0^. For an exhaustive description of the model, see references below.
== References ==
* "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 [arXiv:0803.0481 arXiv:0803.0481]
* "Implementation of the Type III Seesaw model in FeynRules/MadGraph and prospects for discovery with early LHC data", C. Biggio, F. Bonnet, [http://arxiv.org/abs/1107.3463 arxiv:1107.3463].
== Model Files ==
* [http://feynrules.irmp.ucl.ac.be/attachment/wiki/TypeIIISeeSaw/typeIIIseesaw1.1.fr typeIIIseesaw1.1.fr]: this is the file containing the model
* For `MadGraph/MadEvent` and BRIDGE users: [http://feynrules.phys.ucl.ac.be/attachment/wiki/TypeIIISeeSaw/formats.inc formats.inc]: this is a modified version of the file formats.inc, that can be useful when dealing with small mixing angles (the original file sets to zero couplings smaller than 10^-5^)
* [http://feynrules.irmp.ucl.ac.be/attachment/wiki/TypeIIISeeSaw/typeIIIseesaw.nb typeIIIseesaw.nb]: this is a Mathematica notebook that loads the model and export it to the `MadGraph` and `CalcHep` format.
== Validation ==
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 [http://www.lepp.cornell.edu/Research/TPP/BridgeSoftware.html BRIDGE]
* Comparison with the theoretical predictions of the branching ratios calculated with [http://www.lepp.cornell.edu/Research/TPP/BridgeSoftware.html BRIDGE]
* Comparison with previous studies (see [http://arxiv.org/pdf/0805.1613 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^+/-^tr^0^
Details of the validation procedure can be found on [http://arxiv.org/abs/1107.3463 arxiv:1107.3463]. WARNING : Tables 7 and 8 of this paper must be updated due to a bug found in MG4.
== Software ==
The model has been tested on the following machines configurations:
* iMac Intel Core 2 Duo, Mac OS X 10.6.6, FeynRules v1.4.3/FeynRulesv1.6beta, Mathematica 8
* Mac Book Intel Core Duo, Mac OS X 10.4.11, FeynRules v1.4.3, Mathematica 6
We also checked the compatibility of our model with Madgraph version 4 and version 5.
(N.B.: when running this model with mg4 some channels are not generated. Please, use mg5 to have the correct result.)
== Notes ==
We implemented the couplings to Goldstone bosons so the implementation allows for the use of Feynman gauge. We have checked that the exportation to the `CalcHep` format is successful however we did not check the `CalcHep` output.