The B-L model

as a U(1) extension of the SM with 3 RH neutrinos and a singlet scalar.

Implementation authors

• 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.

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.

• Pure B-L model: gt = 0. This is the "pure" version of the model, where the mixing between Z and Z' is set to zero. 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

• ​http://arxiv.org/abs/arXiv:1106.4762 Theoretical constraints on the couplings of non-exotic minimal Z' bosons (full model description in Feynman gauge)

• 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.

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

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Parameter description and user guide

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.