A 4 × U(1)PQ model for the lepton flavor structure and the strong CP problem

  • Takaaki Nomura
  • Yusuke Shimizu
  • Toshifumi Yamada
Open Access
Regular Article - Theoretical Physics


We present a model with A 4 × U(1)PQ lepton flavor symmetry which explains the origin of the lepton flavor structure and also solves the strong CP problem. Standard model gauge singlet fields, so-called “flavons”, charged under the A 4 × U(1)PQ symmetry are introduced and are coupled with the lepton and the Higgs sectors. The flavon vacuum expectation values (VEVs) trigger spontaneous breaking of the A 4 × U(1)PQ symmetry. The breaking pattern of the A 4 accounts for the tri-bimaximal neutrino mixing and the deviation from it due to the non-zero θ 13 angle, and the breaking of the U(1)PQ gives rise to a pseudo-Nambu-Goldstone boson, axion, whose VEV cancels the QCD θ term. We investigate the breaking of the A 4 × U(1)PQ symmetry through an analysis on the scalar potential and further discuss the properties of the axion in the model, including its decay constant, mass and coupling with photons. It is shown that the axion decay constant is related with the right-handed neutrino mass through the flavon VEVs. Experimental constraints on the axion and their implications are also studied.


Beyond Standard Model Discrete Symmetries Global Symmetries Neutrino Physics 


Open Access

This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.


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Copyright information

© The Author(s) 2016

Authors and Affiliations

  • Takaaki Nomura
    • 1
  • Yusuke Shimizu
    • 1
    • 2
  • Toshifumi Yamada
    • 1
  1. 1.School of Physics, KIASSeoulRepublic of Korea
  2. 2.Graduate School of ScienceHiroshima UniversityHigashi-HiroshimaJapan

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