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Register a new userZee and Zee-Babu mechanisms in the minimal 331 model
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We show that the minimal 3-3-1 model cannot accommodate the neutrino masses at tree level using present experimental data. Nevertheless, a modified Zee and the Zee-Babu mechanisms for generating neutrino masses at 1-loop and 2-loop, respectively, are automatically implemented in the minimal 3-3-1 model, without introducing new degrees of freedom to the model. We also present a systematic method for finding solutions to the leptonic sector masses and mixing. As a case study, we accommodate the charged and neutral leptons masses and the PMNS matrix in the 1-loop modified Zee mechanism contained in the minimal 3-3-1 model.
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We propose a two-loop induced Zee-Babu type neutrino mass model at the TeV scale. Although there is no dark matter candidate in the original Zee-Babu model, that is contained in our model by introducing an unbroken discrete $Z_2$ symmetry. The discrepancy between the experimental value of the muon anomalous magnetic moment (muon $g-2$) and its prediction in the standard model can be explained by contributions from additional vector-like charged-leptons which are necessary to give non-zero neutrino masses. The mass of vector-like leptons to be slightly above 300 GeV is favored and allowed from the muon $g-2$ and the current LHC data. We find that from the structure of neutrino mass matrix, doubly-charged scalar bosons in our model can mainly decay into the same-sign and same-flavour dilepton plus missing transverse momentum. By measuring an excess of these events at the LHC, our model can be distinguished from the other models including doubly-charged scalar bosons.
We demonstrate that the extension of the Zee-Babu model can generate not only the small neutrino masses but also the baryon number asymmetry in the universe. In particular, we show that the scale of the singlet scalar responsible for the leptogenesis can be of order 1 TeV, that can be tested at the LHC and ILC. We also considered the possible minimal extension of this model to generate the dark matter.
The Zee model generates neutrino masses at the one-loop level by adding charged SU(2)_L-singlet and extra SU(2)_L-doublet scalars to the standard model of particle physics. As the origin of the nontrivial structure of the lepton flavor mixing, we introduce the softly broken A_4 symmetry to the Zee model. This model is compatible with the tribimaximal mixing which agrees well with neutrino oscillation measurements. Then, a sum rule m_1 e^{i alpha_12} + 2 m_2 + 3 m_3 e^{i alpha_32} = 0 is obtained and it results in Delta m^2_31 < 0 and m_3 > 1.8*10^{-2}eV. The effective mass |(M_nu)_{ee}| for the neutrinoless double beta decay is predicted as | (M_ u)_{ee} | > 1.7*10^{-2}eV. The characteristic particles in this model are SU(2)_L-singlet charged Higgs bosons s^+_alpha (alpha=xi,eta,zeta) which are made from a 3-representation of A_4. Contributions of s^+_alpha to the lepton flavor violating decays of charged leptons are almost forbidden by an approximately remaining Z_3 symmetry; only BR(tau to ebar mu mu) can be sizable by the flavor changing neutral current interaction with SU(2)_L-doublet scalars. Therefore, s^+_alpha can be easily light enough to be discovered at the LHC with satisfying current constraints. The flavor structures of BR(s^-_alpha to ell nu) are also discussed.
We extend the Zee model, where tiny neutrino masses are generated at the one loop level, to a supersymmetric model with R-parity conservation. It is found that the neutrino mass matrix can be consistent with the neutrino oscillation data thanks to the nonholomorphic Yukawa interaction generated via one-loop diagrams of sleptons. We find a parameter set of the model, where in addition to the neutrino oscillation data, experimental constraints from the lepton flavor violating decays of charged leptons and current LHC data are also satisfied. In the parameter set, an additional CP-even neutral Higgs boson other than the standard-model-like one, a CP-odd neutral Higgs boson, and two charged scalar bosons are light enough to be produced at the LHC and future lepton colliders. If the lightest charged scalar bosons are mainly composed of the SU(2)_L-singlet scalar boson in the model, they would decay into e nu and mu nu with 50% of a branching ratio for each. In such a case, the relation among the masses of the charged scalar bosons and the CP-odd Higgs in the minimal supersymmetric standard model approximately holds with a radiative correction. Our model can be tested by measuring the specific decay patterns of charged scalar bosons and the discriminative mass spectrum of additional scalar bosons.
We consider a local $U(1)_{B-L}$ extension of Zee-Babu model to explain the recently observed 3.5 keV X-ray line signal. The model has three Standard model (SM)-singlet Dirac fermions with different $U(1)_{B-L}$ charges. A complex scalar field charged under $U(1)_{B-L}$ is introduced to break the $U(1)_{B-L}$ symmetry. After $U(1)_{B-L}$ symmetry breaking a remnant discrete symmetry stabilizes the lightest state of the Dirac fermions, which can be a stable dark matter (DM). The second lightest state, if mass splitting with the stable DM is about 3.5 keV, decays dominantly to the stable DM and 3.5 keV photon through two-loop diagrams, explaining the X-ray line signal. Two-loop suppression of the decay amplitude makes its lifetime much longer than the age of the universe and it can be a decaying DM candidate in large parameter region. We also introduce a real scalar field which is singlet under both the SM and $U(1)_{B-L}$ and can explain the current relic abundance of the Dirac fermionic DMs. If the mixing with the SM Higgs boson is small, it does not contribute to DM direct detection. The main contribution to the scattering of DM off atomic nuclei comes from the exchange of $U(1)_{B-L}$ gauge boson, $Z$, and is suppressed below current experimental bound when $Z$ mass is heavy ($gtrsim 10$ TeV). If the singlet scalar mass is about 0.1-10 MeV, the DM self-interaction can be large enough to solve small scale structure problems in simulations with the cold DM, such as, the core-vs-cusp problem and too-big-to-fail problem.
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