New Simple A_4 Neutrino Model for Nonzero \theta_{13} and Large \delta_{CP}

In a new simple application of the non-Abelian discrete symmetry $A_4$ to charged-lepton and neutrino mass matrices, we show that for the current experimental central value of $\sin^2 2 \theta_{13} \simeq 0.1$, leptonic CP violation is necessarily large, i.e. $|\tan \delta_{CP}| > 1.3$.Comment: 12 pages, 8 figure

A model of quarks with Delta (6N^2) family symmetry

We propose a first model of quarks based on the discrete family symmetry Delta (6N^2) in which the Cabibbo angle is correctly determined by a residual Z_2 times Z_2 subgroup, and the smaller quark mixing angles may be qualitatively understood from the model. The present model of quarks may be regarded as a first step towards formulating a complete model of quarks and leptons based on Delta (6N^2), in which the lepton mixing matrix is fully determined by a Klein subgroup. For example, the choice N=28 provides an accurate determination of both the reactor angle and the Cabibbo angle.Comment: 12 pages, 5 figures; reference adde

Admixture of quasi-Dirac and Majorana neutrinos with tri-bimaximal mixing

We propose a realization of the so-called bimodal/schizophrenic model proposed recently. We assume S4, the permutation group of four objects as flavor symmetry giving tri-bimaximal lepton mixing at leading order. In these models the second massive neutrino state is assumed quasi-Dirac and the remaining neutrinos are Majorana states. In the case of inverse mass hierarchy, the lower bound on the neutrinoless double beta decay parameter m_ee is about two times that of the usual lower bound, within the range of sensitivity of the next generation of experiments.Comment: 8 pages, minor changes to match version accepted in PL

CP Phases of Neutrino Mixing in a Supersymmetric B-L Gauge Model with T_7 Lepton Flavor Symmetry

In a recently proposed renormalizable model of neutrino mixing using the non-Abelian discrete symmetry T_7 in the context of a supersymmetric extension of the Standard Model with gauged U(1)_{B-L}, a correlation was obtained between \theta_{13} and \theta_{23} in the case where all parameters are real. Here we consider all parameters to be complex, thus allowing for one Dirac CP phase \delta_{CP} and two Majorana CP phases \alpha_{1,2}. We find a slight modification to this correlation as a function of \delta_{CP}. For a given set of input values of \Delta m^2_{21}, \Delta m^2_{32}, \theta_{12}, and \theta_{13}, we obtain \sin^2 2 \theta_{23} and m_{ee} (the effective Majorana neutrino mass in neutrinoless double beta decay) as functions of \tan \delta_{CP}. We find that the structure of this model always yields small |\tan \delta_{CP}|.Comment: 15 pages, 10 figure

S4 Flavor Model of Quarks and Leptons

We present an $S_4$ flavor model to unify quarks and leptons in the framework of the SU(5) GUT. Three generations of $\bar 5$-plets in SU(5) are assigned $3_1$ of $S_4$ while the first and the second generations of 10-plets in SU(5) are assigned to be 2 of $S_4$, and the third generation of 10-plet is to be $1_1$ of $S_4$. Right-handed neutrinos are also assigned 2 for the first and second generations and $1_1$ for the third generation, respectively. Taking vacuum alignments of relevant gauge singlet scalars, we predict the quark mixing as well as the tri-bimaximal mixing of neutrino flavors. Especially, the Cabbibo angle is predicted to be $15^{\circ}$ in the limit of the vacuum alignment. We can improve the model to predict observed CKM mixing angles.Comment: 11 pages, talked at the 16th Yukawa International Seminar, Particle Physics beyond the Standard Mode

Minimal seesaw model with S_4 flavor symmetry

We discuss a neutrino mass model based on the S_4 flavor symmetry within the minimal seesaw framework, in which only two right-handed neutrinos are introduced and transform as 2 under S_4. Although the model contains less free parameters compared to the typical seesaw models, it provides a successful description of the observed neutrino parameters, and in particular, a nearly tri-bimaximal mixing pattern can be naturally accommodated. In addition, the heavy right-handed neutrino masses are found to be non-degenerate, while only the normal hierarchical mass spectrum is compatible with experiments for light neutrinos.Comment: 8 pages, 4 figures; version to appear in PL

Like-sign dimuon asymmetry of B0 meson and LFV in SU(5) SUSY GUT with S4 flavor symmetry

The like-sign dimuon charge asymmetry of the $B$ meson, which was reported in the D\O Collaboration, is studied in the SU(5) SUSY GUT model with $S_4$ flavor symmetry. Additional CP violating effects from the squark sector are discussed in $B_s-\bar B_s$ mixing process. The predicted like-sign charge asymmetry is in the 2$\sigma$ range of the combined result of D\O and CDF measurements. Since the SUSY contributions in the quark sector affect to the lepton sector because of the SU(5) GUT relation, two predictions are given in the leptonic processes: (i) both ${\rm BR}(\mu \to e \gamma)$ and the electron EDM are close to the present upper bound, (ii) the decay ratios of $\tau$ decays, $\tau \to \mu\gamma$ and $\tau \to e \gamma$, are related to each other via the Cabibbo angle $\lambda_c$: {\rm BR}(\tau \to e\gamma)/{\rm BR}(\tau \to \mu\gamma)\sime \lambda_c^2. These are testable at future experiments.Comment: 33 pages, 4 figures, a footnote and references are adde

Tri-bimaximal Mixing and Cabibbo Angle in S4 Flavor Model with SUSY

We present a flavor model of quarks and leptons with the non-Abelian discrete symmetry $S_4$ in the framework of the SU(5) SUSY GUT. Three generations of $\bar 5$-plets in SU(5) are assigned to ${\bf 3}$ of $S_4$ while the first and second generations of 10-plets in SU(5) are assigned to ${\bf 2}$ of $S_4$, and the third generation of 10-plet is assigned to ${\bf 1}$ of $S_4$. Right-handed neutrinos are also assigned to ${\bf 2}$ for the first and second generations and ${\bf 1}'$ for the third generation. We predict the Cabibbo angle as well as the tri-bimaximal mixing of neutrino flavors. We also predict the non-vanishing $U_{e3}$ of the neutrino flavor mixing due to higher dimensional mass operators. Our predicted CKM mixing angles and the CP violation are consistent with experimental values. We also study SUSY breaking terms in the slepton sector. Our model leads to smaller values of flavor changing neutral currents than the present experimental bounds.Comment: 32 pages, 4 figures, some references are added, with minor modificatio