arXiv subjects
Publications and source records attributed to Morimitsu Tanimoto.
We study the supersymmetric model with $D_4 \times Z_2$ lepton flavor symmetry. We evaluate soft supersymmetry breaking terms, i.e. soft slepton masses and A-terms, which are predicted in the $D_4$ flavor model. We consider constraints due to experiments of flavor changing neutral current processes.
We present the $D_4\times Z_2$ flavor symmetry, which is different from the previous work by Grimus and Lavoura. Our model reduces to the standard model in the low energy and there is no FCNC at the tree level. Putting the experimental data, parameters are fixed, and then the implication of our model is discussed. The condition to realize the tri-bimaximal mixing is presented. The possibility for stringy realization of our model is also discussed.
The tri-bimaximal mixing is a good approximation for the present data of neutrino mixing angles. The deviation from the tri-bimaximal mixing is discussed numerically in the framework of the A4 model. Values of \tan^2θ_{12}, \sin^2 2θ_{23} and |U_{e3}| deviate from the tri-bimaximal mixing due to the corrections of the vacuum alignment of flavon fields. It is remarked that \sin^2 2θ_{23} deviates scarcely from 1 while \sin^2θ_{12} can deviate from 1/3 considerably and \sinθ_{13} could be near the present experimental upper bound. The CP violating measure J_{CP} and the effective Majorana neutrino mass m_{ee} are also discussed.
We present detailed analyses of the vacuum structure of the scalar potential in a supersymmetric Mass Varying Neutrinos model. The observed dark energy density is identified with false vacuum energy and the dark energy scale of order $(10^{-3}eV)^4$ is understood by gravitationally suppressed supersymmetry breaking scale, $F({TeV})^2/M_{Pl}$, in the model. The vacuum expectation values of sneutrinos should be tiny in order that the model works. Some decay processes of superparticles into acceleron and sterile neutrino are also discussed in the model.
We consider a Mass Varying Neutrinos (MaVaNs) model in supersymmetric theory. The model includes effects of supersymmetry breaking transmitted by the gravitational interaction from the hidden sector, in which supersymmetry was broken, to the dark energy sector. Then evolutions of the neutrino mass and the equation of state parameter of the dark energy are presented in the model. It is remarked that only the mass of a sterile neutrino is variable in the case of the vanishing mixing between the left-handed and a sterile neutrino on cosmological time scale. The finite mixing makes the mass of the left-handed neutrino variable.
A texture-zeros is an approach to reduce the number of free parameters in Yukawa couplings and it is one of the most attractive ones. In our paper, we discuss the origin of zero-structure in texture-zeros by S_3 flavor symmetry approach. Some of electroweak doublet Higgs fields have vanishing vacuum expectation value(VEV) which leads to vanishing elements in quark and lepton mass matrices. Then, the structure of supersymmetric scalar potential is analyzed and Higgs fields have non-trivial S_3 charges. As a prediction of our paper, a lower bound of a MNS matrix element, U_{e3} \geq 0.04, is obtained. The suppression of flavor-changing neutral currents(FCNC) mediated by the Higgs fields is discussed and lower bounds of the Higgs masses are derived.
The comprehensive analyses are presented in the model with the inverted mass hierarchy for neutrinos, which follows from a geometrical structure of a (1+5) dimensional space-time where two extra dimensions are compactified on the T^2/Z_3 orbifold. The model gives two large lepton flavor mixings due to the S3 structure in the (1+5) dimensional space-time. It also predicts the lightest neutrino mass as m_3=(1-50)\times 10^{-5}eV and the effective neutrino mass responsible for neutrinoless double beta decays as _{ee}\simeq 50 meV. The low energy CP violation, J_{CP} could be 0.02. On the other hand, the observed baryon asymmetry in the present universe is produced by the non-thermal leptogenesis, which works even at the reheating temperature TR=10^{4}-10^{6}GeV. The correlation between the baryon asymmetry and the low energy CP violation is examined in this model.
The mass matrix forms of quarks and leptons are discussed in theory with permutation flavor symmetry. The structure of scalar potential is analyzed in case that electroweak doublet Higgs fields have non-trivial flavor symmetry charges. We find that realistic forms of mass matrices are obtained dynamically in the vacuum of the theory, where some of Higgs bosons have vanishing expectation values which lead to vanishing elements in quark and lepton mass matrices. Mass textures are realized in the true vacuum and their positions are controlled by flavor symmetry. An interesting point is that, due to the flavor group structure, the up and down quark mass matrices are automatically made different in the vacuum, which lead to non-vanishing generation mixing. It is also discussed that flavor symmetry is needed to be broken in order not to have too light scalars. The lower bounds of Higgs masses are derived from the experimental data of flavor-changing rare processes such as the neutral K meson mixing.
The mass matrix forms of quarks and leptons are discussed in theory with permutation flavor symmetry. The structure of scalar potential is analyzed in case that electroweak doublet Higgs fields have non-trivial flavor symmetry charges. We find that realistic forms of mass matrices are obtained dynamically in the vacuum of the theory, where some of Higgs bosons have vanishing expectation values which lead to vanishing elements in quark and lepton mass matrices. An interesting point is that, due to the flavor group structure, the up and down quark mass matrices are automatically made different in the vacuum, which lead to non-vanishing generation mixing. It is also discussed that flavor symmetry is needed to be broken in order not to have too light scalars.
We discuss the effect of the supersymmetry breaking on the Mass Varying Neutrinos(MaVaNs) scenario. Especially, the effect mediated by the gravitational interaction between the hidden sector and the dark energy sector is studied. A model including a chiral superfield in the dark sector and the right-handed neutrino superfield is proposed. Evolutions of the neutrino mass and the equation of state parameter are presented in the model.
The successful A4 family symmetry for leptons is applied to quarks, motivated by the quark-lepton assignments of SU(5). Realistic quark masses and mixing angles are obtained, in good agreement with data. In particular, we find a strong correlation between |V_{ub}| and the CP phase beta, thus allowing for a decisive future test of this model.
We study the SUSY SO(10) GUT with the symmetric two-zero textures of quark/lepton mass matrix which realize the Georgei-Jarlskog relations in down-type quark and charged lepton masses. We show that the important constraints to such framework come from the bottom-tau unification and the observed value of $\sin2β$, one of the angles in the CKM unitarity triangle. We investigate the symmetric two-zero textures assumed at the GUT scale by solving the MSSM renormalization group equations with right-handed neutrino threshold effects. As a result, the value of $\tan\tildeβ$ is constrained to be large enough and the representation of Higgs field which couples to the third generation of left- and right-handed neutrinos is restricted by the bottom-tau unification condition. The textures with vanishing 1-2 (and 2-1) element for up-type quarks and vanishing 1-3 (and 3-1) element for down-type quarks are favored by the observation of $\sin2β$.
We discuss about the speed of sound squared in the Mass Varying Neutrinos scenario (MaVaNs). Recently, it was argued that the MaVaNs has a catastrophic instability which is the emergence of an imaginary speed of sound at the non-relativistic limit of neutrinos. As the result of this instability, the neutrino-acceleron fluid cannot act as the dark energy. However, it is found that the speed of sound squared in the neutrino-acceleron fluid could be positive in our model. We examine the speed of sound in two cases of the scalar potential. One is the small fractional power-law potential and another is the logarithmic one. The power-law potential model with the right-handed neutrinos gives a stable one.
We have embedded the texture of the neutrino mass matrix with three families into the MaVaNs scenario. We take the power-law potential of the acceleron field and a typical texture of active neutrinos, which is derived by the D_4 symmetry and predicts the maximal mixing of the atmospheric neutrino and the vanishing U_{e3}. The effect of couplings among the dark fermion and active neutrinos are studied by putting the current cosmological data and the terrestrial neutrino experimental data. It is found that the neutrino flavor mixings evolve as well as the neutrino masses. Especially, U_{e3} develops into the non-vanishing one and θ_{atm} deviates from the maximal mixing due to couplings among the dark fermion and active neutrinos.
We discuss the mass varying neutrino scenario in the supersymmetric theory. In the case of the model with the single superfield, one needs the soft SUSY breaking terms or the $μ$ term. However, fine-tunings of some parameters are required to be consistent with the cosmological data. In order to avoid the fine-tuning, we discuss the model with two superfields, which is consistent with the cosmological data. However, it is found that the left-handed neutrino mixes with the neutrino of the dark sector maximally. Adding a right- handed neutrino, which does not couple to the dark sector, we obtain a favorable model in the phenomenology of the neutrino experiments. In this model, the deceleration of the cosmological expansion converts to the acceleration near $z\simeq 0.5$. The speed of sound $c_s$ becomes imaginary if we put $ω_0=-0.9$, which corresponds to $m_ν^0=3.17\eV$. On the other hand, if we take $ω_0=-0.998$, which leads to $m_ν^0=0.05\eV$, $c_s^2$ becomes positive since $ω$ evolves rapidly near the present epoch in our model.
Using the seesaw mechanism and a discrete symmetry, we construct a class of models for the neutrino mass matrix where the inverse of that matrix is the sum of a mu-tau antisymmetric background and a perturbation. We consider various possibilities for that perturbation. The simplest possible perturbations lead to four-parameter neutrino mass matrices which are unable to fit the experimental data. More complicated perturbations give rise to viable six-parameter mass matrices; we present detailed predictions of each of them.
We present numerical and comprehensive analyses of the sixty hybrid textures of neutrinos, which have an equality of matrix elements and one zero. These textures are possibly derived from the discrete symmetry. Only six textures among sixty ones are excluded by the present experimental data. Since there are many textures which give similar predictions, the textures are classified based on the numerical results. The neutrinoless double beta decay is also examined in these textures. Our results suggest that there remain still rich structures of the neutrino mass matrix in the phenomenological point of view.
We discuss the question why the mixing $U_{e3}$ is small. The natural answer is $U_{e3}=0$ in some symmetric limit, in which two large mixings are realized. It is possible to force $U_{e3}$ and $\cos{2 θ_{23}}$ to be zero by imposing a discrete symmetry. We investigate a special class of symmetries $Z_2$ and of the consequences of their perturbative violation.