'''The B-L model'''
 as a U(1) extension of the SM with 3 RH neutrinos and a singlet scalar.

This is an update to the previous minimal Zprime model.

** Implementation authors

* This version
 * Wei Liu
  * Department of Physics & Astronomy, University College London
  * wei.liu.16 -at- ucl.ac.uk
  * update based on Lorenzo Basso's model with availability to FeynRules 2.3 with the help of Dr. Frank Deppisch.

* Previous version
 * Lorenzo Basso
  * Physikalisches Institut, Albert-Ludwigs-Universität Freiburg (Germany)
  * lorenzo.basso -at- physik.uni-freiburg.de
  * (formerly at University of Southampton, UK & RAL-PPD, Didcot, UK)
  * Based upon the minimal B-L model implementation, done in collaboration with Giovanni Marco Pruna (TU Dresden, Institut für Kern- und Teilchenphysik, Dresden, Germany, formerly at University of Southampton, UK & RAL-PPD, Didcot, UK).



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** Model description

The model describe a U(1) extension of the SM, related to the B-L (baryon minus lepton) charge. 3 RH neutrinos are required to cancel the anomalies, thus providing neutrino masses via the type-I see-saw. A Z' boson is also present, together with a further scalar for the spontaneous symmetry breaking of the further U(1) factor, at TeV scale.


 - Minimal B-L model: gt = 0. This is the "Minimal" version of the model, where the mixing between Z and Z' is set to zero. This choice is set for the .fr and UFO file.
 {{{#!comment

This model describes a 1-dimensional class of Z' models, where a continuous parameter scans over the possible discrete models. The model is fully implemented in the Feynman gauge (also Goldstones and Ghosts).

Popular benchmark models from the literature are recovered by setting appropriated relations among the new gauge parameters.
Separate model files for this benchmark model exists.
- SO(10)-inspired U(1)_chi: gt = - 4/5 g1p.
 - U(1)_R: gt = -2 g1p.
}}}

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** References
* Please cite https://arxiv.org/abs/1811.11452, https://arxiv.org/abs/1804.04075 and http://arxiv.org/abs/arXiv:0812.4313 for using this version of the model.
* This version
 * https://arxiv.org/abs/1811.11452 LHC Constraints on a B-L Gauge Model using Contur 
 * https://arxiv.org/abs/1804.04075 Long-lived Heavy Neutrinos from Higgs Decays (The study of the parameter space in the neutrino sector)
* Previous version
 * For the pure B-L benchmark see also http://arxiv.org/abs/arXiv:0812.4313 Phenomenology of the minimal B-L extension of the Standard model: Z' and neutrinos.
 * http://arxiv.org/abs/arXiv:1106.4762 Theoretical constraints on the couplings of non-exotic minimal Z' bosons (full model description in Feynman gauge)
 * Details about available parameter space and experimental/theoretical constraints can be found in:
 * http://arxiv.org/abs/arXiv:1002.1939 Tree Level Unitarity Bounds for the Minimal B-L Model
 * http://arxiv.org/abs/arXiv:1002.3586 Z' discovery potential at the LHC in the minimal B-L extension of the Standard Model
 * http://arxiv.org/abs/arXiv:1004.3039 A Renormalisation Group Equation Study of the Scalar Sector of the Minimal B-L Extension of the Standard Model
 * http://arxiv.org/abs/arXiv:1011.2612 Phenomenology of the minimal B−L extension of the Standard Model: the Higgs sector





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** Model files

See attachments

*Please use BL_N_UFO when use display modellist at MadGraph, otherwise it would not be a valid path name.

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** Parameter description and user guide

The choice of benchmark model within the class is done by choosing the free parameters below. 

Free parameters
* Scalar sector
 * Higgs mixing angle, sa
 * The mass of the Higgs, mh1 and mh2, where mh1 is usually the mass of the SM model Higgs. 
* Gauge boson sector
 * The Z' boson mass, mzp
 * The coupling constant of B-L group, g1p
* Neutrino sector
 * The heavy neutrino mass, mnh1, mnh2 and mnh3
 * The light neutrino mass, mnl1, mnl2 and mnl3
 * The neutrino mixing matrix are internal parameter set by Type-I seesaw, please read http://arxiv.org/abs/arXiv:0812.4313.
* Please set the decay width of the heavy neutrino, two Higgs and Z' to auto (in MadGraph5 param_card.dat)
 {{{#!comment

The choice of benchmark model within the class is done by selecting the appropriate relation between the new gauge couplings. "g1p" is the gauge coupling directly connected to the U(1)_{B-L} group (also present in the minimal B-L model files), "gt" is the mixing parameter. Because of the limited number of degrees of freedom, the Z' mass has been chosen as the last free parameter, adjustable by the user. Therefore, the mixing Z-Z' angle, the B-L-breaking vev and the Z-boson are INTERNAL parameters, evaluated as a function of the input parameters (g1p, gt, MZp). Henceforth, it's up to the user to choose values for the independent parameter complying to experimental constraints to ensure not to spoil in particular the Z mass. Per given benchmark model, it is sufficient to choose a Zp mass allowed by the LEP constraints to obtain a Z mass compatible with the LEP measurement, within errors.
}}}