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Register a new userProbing neutrino and Higgs sectors in $SU(2)_1 times SU(2)_2 times U(1)_Y$ model with lepton-flavor non-universality
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The neutrino and Higgs sectors in the $mbox{SU(2)}_1 times mbox{SU(2)}_2 times mbox{U(1)}_Y $ model with lepton-flavor non-universality are discussed. We show that active neutrinos can get Majorana masses from radiative corrections, after adding only new singly charged Higgs bosons. The mechanism for generation of neutrino masses is the same as in the Zee models. This also gives a hint to solving the dark matter problem based on similar ways discussed recently in many radiative neutrino mass models with dark matter. Except the active neutrinos, the appearance of singly charged Higgs bosons and dark matter does not affect significantly the physical spectrum of all particles in the original model. We indicate this point by investigating the Higgs sector in both cases before and after singly charged scalars are added into it. Many interesting properties of physical Higgs bosons, which were not shown previously, are explored. In particular, the mass matrices of charged and CP-odd Higgs fields are proportional to the coefficient of triple Higgs coupling $mu$. The mass eigenstates and eigenvalues in the CP-even Higgs sector are also presented. All couplings of the SM-like Higgs boson to normal fermions and gauge bosons are different from the SM predictions by a factor $c_h$, which must satisfy the recent global fit of experimental data, namely $0.995<|c_h|<1$. We have analyzed a more general diagonalization of gauge boson mass matrices, then we show that the ratio of the tangents of the $W-W$ and $Z-Z$ mixing angles is exactly the cosine of the Weinberg angle, implying that number of parameters is reduced by 1. Signals of new physics from decays of new heavy fermions and Higgs bosons at LHC and constraints of their masses are also discussed.
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The lepton masses and mixings are studied on the basis of string inspired $SU(6)times SU(2)_R$ model with global flavor symmetries. Provided that sizable mixings between lepton doublets $L$ and Higgsino-like fields $H_d$ with even R-parity occur and that seesaw mechanism is at work in the neutrino sector, the model can yield a large mixing angle solution with $tan theta_{12}, tan theta_{23} = O(sqrt{l})$ $({l}= 0.22)$, which is consistent with the recent experimental data on atmospheric and solar neutrinos. In the solution Dirac mass hierarchies in the neutrino sector cancel out with the heavy Majorana sector in large part due to seesaw mechanism. Hierarchical pattern of charged lepton masses can be also explained.
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In this paper, we attempt to build an unified model with democratic texture, that have some unification between $Y_{ u}$ and $Y_{u}$. Since the $S_{3L} times S_{3R}$ flavor symmetry is chiral, the unified gauge group is assumed to be Pati-Salam type $SU(4)_{c} times SU(2)_{L} times SU(2)_{R}$. The flavor symmetry breaking scheme is considered to be $S_{3L} times S_{3R} to S_{2L} times S_{2R} to 0$. In this picture, the four-zero texture is desirable for realistic mass and mixings. This texture is realized by a specific representation for the second breaking of the $S_{3L} times S_{3R}$ flavor symmetry. Assuming only renormalizable Yukawa interactions, type-I seesaw mechanism, and neglecting $CP$ phases for simplicity, the right-handed neutrino mass matrix $M_{R}$ can be reconstructed from low energy input values. Numerical analysis shows that the texture of $M_{R}$ basically behaves like the waterfall texture. Since $M_{R}$ tends to be the cascade texture in the democratic texture approach, a model with type-I seesaw and up-type Yukawa unification $Y_{ u} simeq Y_{u}$ basically requires fine-tunings between parameters. Therefore, it seems to be more realistic to consider universal waterfall textures for both $Y_{f}$ and $M_{R}$, e.g., by the radiative mass generation or the Froggatt--Nielsen mechanism. Moreover, analysis of eigenvalues shows that the lightest mass eigenvalue $M_{R1}$ is too light to achieve successful thermal leptogenesis. Although the resonant leptogenesis might be possible, it also requires fine-tunings of parameters.
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