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Register a new userFermion Mass and Mixing in a Low-Scale Seesaw Model based on the S4 Flavor Symmetry
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We construct a low-scale seesaw model to generate the masses of active neutrinos based on $S_4$ flavor symmetry supplemented by the $Z_2 times Z_3 times Z_4 times Z_{14}times U(1)_L$ group, capable of reproducing the low energy Standard model (SM) fermion flavor data. The masses of the SM fermions and the fermionic mixings parameters are generated from a Froggatt-Nielsen mechanism after the spontaneous breaking of the $S_4times Z_2 times Z_3 times Z_4 times Z_{14}times U(1)_L$ group. The obtained values for the physical observables of the quark and lepton sectors are in good agreement with the most recent experimental data. The leptonic Dirac CP violating phase $de _{CP}$ is predicted to be $259.579^circ$ and the predictions for the absolute neutrino masses in the model can also saturate the recent constraints.
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We study a neutrino mass model based on $S_4$ flavor symmetry which accommodates lepton mass, mixing with non-zero $theta_{13}$ and CP violation phase. The spontaneous symmetry breaking in the model is imposed to obtain the realistic neutrino mass and mixing pattern at the tree- level with renormalizable interactions. Indeed, the neutrinos get small masses from one $SU(2)_L$ doubplet and two $SU(2)_L$ singlets in which one being in $underline{2}$ and the two others in $underline{3}$ under $S_4$ with both the breakings $S_{4}rightarrow S_3$ and $S_{4}rightarrow Z_3$ are taken place in charged lepton sector and $S_4rightarrow mathcal{K}$ in neutrino sector. The model also gives a remarkable prediction of Dirac CP violation $delta_{CP}=frac{pi}{2}$ or $-frac{pi}{2}$ in the both normal and inverted spectrum which is still missing in the neutrino mixing matrix. The relation between lepton mixing angles is also represented.
A simple Standard Model Extension based on $T_7$ flavor symmetry which accommodates lepton mass and mixing with non-zero $theta_{13}$ and CP violation phase is proposed. At the tree- level, the realistic lepton mass and mixing pattern is derived through the spontaneous symmetry breaking by just one vacuum expectation value ($v$) which is the same as in the Standard Model. Neutrinos get small masses from one $SU(2)_L$ doublet and two $SU(2)_L$ singlets in which one being in $underline{1}$ and the two others in $underline{3}$ and $underline{3}^*$ under $T_7$ , respectively. The model also gives a remarkable prediction of Dirac CP violation $delta_{CP}=172.598^circ$ in both normal and inverted hierarchies which is still missing in the neutrino mixing matrix.
We propose a hybrid seesaw model based on $A_{4}$ flavor symmetry, which generates a large hierarchical flavor structure. In our model, tree-level and one-loop seesaw mechanisms predict different flavor structures in the neutrino mass matrix, and generate a notable hierarchy among them. We find that such a hierarchical structure gives a large effective neutrino mass which can be accessible by next-generation neutrinoless double beta decay experiments. Majorana phases can also be predictable. The $A_{4}$ flavor symmetry in the model is spontaneously broken to the $Z_{2}$ symmetry, leading to a dark matter candidate which is assumed to be a neutral scalar field. The favored mass region of the dark matter is obtained by numerical computations of the relic abundance and the cross section of the nucleon. We also investigate the predictions of the several hierarchical flavor structures based on $A_{4}$ symmetry for the effective neutrino mass and the Majorana phases, and find the characteristic features depending on the hierarchical structures.
We study lepton flavor number violating rare B decays, $b to s l_h^{pm} l_l^{mp}$, in a seesaw model with low scale singlet Majorana neutrinos motivated by the resonant leptogenesis scenario. The branching ratios of inclusive decays $ b to s l_h^{pm} bar{l_l}^{mp} $ with two almost degenerate singlet neutrinos at TeV scale are investigated in detail. We find that there exists a class of seesaw model in which the branching fractions of $ b to s tau mu $ and $tau to mu gamma$ can be as large as $10^{-10}$ and $10^{-9}$ within the reach of Super B factories, respectively, without being in conflict with neutrino mixings and mass squared difference of neutrinos from neutrino data, invisible decay width of $Z$ and the present limit of $Br(mu to e gamma)$.
In a recently proposed multi-Higgs extension of the standard model in which discrete symmetries, $A_4$ and $Z_3$ are imposed we show that, after accommodating the fermion masses and the mixing matrices in the charged currents, the mixing matrices in the neutral currents induced by neutral scalars are numerically obtained. However, the flavor changing neutral currents are under control mainly by mixing and/or mass suppressions in the neutral scalar sector.
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