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We present a renormalizable flavor model with Z_4 as flavor symmetry in both the quark and lepton sectors. The model is constructed with a minimal approach and no-right handed neutrinos are introduced. In this approach a minimum number of two SU(2) Higgs doublets and one scalar singlet are required in order to obtain the Nearest Neighbor Interaction form for charged fermions and to generate neutrino masses radiatively. For the quark sector we follow the charge assignations made by Branco et. al. in reference [1]. All fermion masses and mixing angles in the model are in agreement with current experimental data and only the inverted hierarchy for the neutrino mass spectrum is allowed. Since neutrinos are Majorana the contribution to neutrinoless double beta decay is also analyzed.
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A new model for tiny neutrino masses is proposed in the gauge theory of $SU(3)_C otimes SU(3)_L otimes U(1)_X$, where neutrino masses are generated via the quantum effect of new particles. In this model, the fermion content is taken to be minimal to realize the gauge anomaly cancellation, while the scalar sector is extended from the minimal 3-3-1 model to have an additional $SU(3)_L$ triplet field. After $SU(3)_Lotimes U(1)_X$ is broken into $SU(2)_Lotimes U(1)_Y$, the Zee model like diagrams are naturally induced, which contain sufficient lepton flavor violating interactions to reproduce current neutrino oscillation data. Furthermore, the remnant $Z_2$ symmetry appears after the electroweak symmetry breaking, which guarantees the stability of dark matter. It is confirmed that this model can satisfy current dark matter data. As an important prediction to test this model, productions and decays of doubly-charged scalar bosons at collider experiments are discussed in successful benchmark scenarios.
Randall Sundrum models provide a possible explanation of (gauge-gravity) hierarchy, whereas discrete symmetry flavor groups yield a possible description of the texture of Standard Model fermion masses. We use both these ingredients to propose a five-dimensional extension of the Standard Model where the mass hierarchy of the four-dimensional effective field theory is obtained only using localizations parameters of order 1. We consider a bulk custodial gauge symmetry group together with an Abelian $Z_4$ group: the model turns out to yield a rather minimal extension of the SM as it only requires two brane Higgs fields to provide the desired Yukawa interactions and the required spontaneous symmetry breaking pattern. In fact, the presence of an extra-dimension allows the use of the Scherk-Schwarz mechanism to contribute to the breaking of the bulk custodial group down to the SM gauge symmetry. Moreover, no right-handed neutrinos are present and neutrino masses are generated radiatively with the help of a bulk charged scalar field that provides the Lepton-number violation. Using experimental inputs from the Global Neutrino Analysis and recent Daya Bay results, a numerical analysis is performed and allowed parameter regions are displayed.
We revisit the current experimental bounds on fourth-generation Majorana neutrino masses, including the effects of right handed neutrinos. Current bounds from LEPII are significantly altered by a global analysis. We show that the current bounds on fourth generation neutrinos decaying to eW and mu W can be reduced to about 80 GeV (from the current bound of 90 GeV), while a neutrino decaying to tau W can be as light as 62.1 GeV. The weakened bound opens up a neutrino decay channel for intermediate mass Higgs, and interesting multi-particle final states for Higgs and fourth generation lepton decays.
We construct a multiscalar and nonrenormalizable $B-L$ model with $A_4times Z_3times Z_4$ flavor symmetry which successfully explains the recent $3+1$ active-sterile neutrino data. The tiny neutrino mass the mass hierarchy are obtained by the type-I seesaw mechanism. The hierarchy of the lepton masses is satisfied by a factor of $v_H left(frac{v_l}{Lambda}right)^2 sim 10^{-4}, mathrm{GeV}$ of the electron mass compared to the muon and tau masses of the order of $frac{v_H v_l}{Lambda} sim 10^{-1}, mathrm{GeV}$. The recent $3+1$ active-sterile neutrino mixings are predicted to be $0.015 leq|U_{e 4}|^2leq 0.045$, $0.004 leq|U_{mu 4}|^2leq 0.012$, $0.004 leq|U_{tau 4}|^2leq 0.014$ for normal hierarchy and $0.020leq|U_{e 4}|^2leq 0.045$, $0.008 leq|U_{mu 4}|^2leq 0.018$, $0.008leq|U_{tau 4}|^2leq 0.022$ for inverted hierarchy. Sterile neutrino masses are predicted to be $0.7 lesssim m_s , (mathrm{eV}) lesssim 3.16$ for normal hierarchy and $2.6 lesssim m_s , (mathrm{eV}) lesssim 7.1$ for inverted hierarchy. For three neutrino scheme the model predicts $0.3401 leq sin^2theta_{12}leq 0.3415, , 0.460 leq sin^2theta_{23}leq 0.540,, -0.60 leq sindelta_{CP}leq -0.20$ for normal hierarchy and $0.3402 leq sin^2theta_{12}leq 0.3416,, 0.434leqsin^2theta_{23}leq 0.610,, -0.95 leq sindelta_{CP}leq -0.60$ for inverted hierarchy. The effective neutrino masses are predicted to be $35.70 leq langle m_{ee}rangle [mbox{meV}] leq 36.50$ in 3+1 scheme and $3.65 leq langle m^{(3)}_{ee}rangle [mbox{meV}] leq 4.10$ in three neutrino scheme for NH while $160.0 leq langle m_{ee}rangle [mbox{meV}] leq 168.0$ in 3+1 scheme and $47.80 leq langle m^{(3)}_{ee}rangle [mbox{meV}] leq 48.70$ in three neutrino scheme for for IH which are all in agreement with the recent experimental data.
In the framework of a left-right model containing mirror fermions with gauge group SU(3)$_{C} otimes SU(2)_{L} otimes SU(2)_{R} otimes U(1)_{Y^prime}$, we estimate the neutrino masses, which are found to be consistent with their experimental bounds and hierarchy. We evaluate the decay rates of the Lepton Flavor Violation (LFV) processes $mu rightarrow e gamma$, $tau rightarrow mu gamma$ and $tau rightarrow egamma$. We obtain upper limits for the flavor-changing branching ratios in agreement with their present experimental bounds. We also estimate the decay rates of heavy Majorana neutrinos in the channels $N rightarrow W^{pm} l^{mp}$, $N rightarrow Z u_{l}$ and $N rightarrow H u_{l}$, which are roughly equal for large values of the heavy neutrino mass. Starting from the most general Majorana neutrino mass matrix, the smallness of active neutrino masses turns out from the interplay of the hierarchy of the involved scales and the double application of seesaw mechanism. An appropriate parameterization on the structure of the neutrino mass matrix imposing a symmetric mixing of electron neutrino with muon and tau neutrinos leads to Tri-bimaximal mixing matrix for light neutrinos.
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