arXiv subjects
Publications and source records attributed to M. Tanimoto.
How is CP violation of low energy related to CP violation required from baryon number asymmetry ? We give an example which shows a direct link between CP violation of neutrino oscillation and baryogenesis through leptogenesis.
We study the correlation between CP violation in neutrino oscillations and leptogenesis in the framework with two heavy Majorana neutrinos and three light neutrinos. Among three unremovable CP phases, a heavy Majorana phase contributes to leptogenesis. We show how the heavy Majorana phase contributes to Jarlskog determinant $J$ as well as neutrinoless double $β$ decay by identifying a low energy CP violating phase which signals the CP violating phase for leptogenesis. For some specific cases of the Dirac mass term of neutrinos, a direct relation between lepton number asymmetry and $J$ is obtained. For the most general case of the framework, we study the effect on $ J $ coming from the phases which are not related to leptogenesis, and also show how the correlation can be lost in the presence of those phases.
We study the see-saw realization of seven textures of the neutrino mass matrix, which were presented by Frampton, Glashow and Marfatia. Two of them B_1 and B_2 are not realized in the see-saw mechanism without fine-tuning of parameters. We present some specific textures of the Dirac neutrino mass matrix and the right-handed Majorana neutrino one. In order to test these textures, we discuss the effect on the branching ratio of mu --> e gamma. We also study the U(1)_X times U(1)_{X'} flavor symmetry, in which U(1)_X is anomalous and U(1)_{X'} is non-anomolous, to reproduce texture zeros. We present examples of U(1) charges for two textures A_1 and A_2$.
We have studied how observables of the neutrino mixing matrix can link up with the ones in the quark sector. The deviation from the bi-maximal flavor mixing is parameterized using a 3 x 3 unitary matrix. The neutrino mixings are investigated supposing this unitary matrix to be hierarchical like the quark mixing matrix. We obtain the remarkable prediction |U_{e3}| >= 0.03 from the experimentally allowed range tan^2 theta_{sol} = 0.24 ~ 0.89. The CP violation in neutrino oscillations is expected to be very small.
We investigate the lepton flavor violation in the framework of the MSSM with right-handed neutrinos taking the large mixing angle MSW solution in the quasi-degenerate and the inverse-hierarchical neutrino masses. We predict the branching ratio of $μ\to e+γ$ and $τ\to μ+γ$ processes assuming the degenerate right-handed Majorana neutrino masses. We find that the branching ratio in the quasi-degenerate neutrino mass spectrum is 100 times smaller than the ones in the inverse-hierarchical and the hierarchical neutrino spectra. We emphasize that the magnitude of $U_{e3}$ is one of important ingredients to predict BR($μ\to e +γ$). The effect of the deviation from the complete-degenerate right-handed Majorana neutrino masses are also estimated. Furtheremore, we examine the $S_{3\sL}\times S_{3\sR}$ model, which gives the quasi-degenerate neutrino masses, and the Shafi-Tavartkiladze model, which gives the inverse-hierarchical neutrino masses. Both predicted branching ratios of $μ\to e+γ$ are smaller than the experimantal bound.
We have investigated the lepton flavor violation in the supersymmetric framework assuming the large mixing angle MSW solution with the quasi-degenerate and the inverse-hierarchical neutrino masses. In the case of the quasi-degenerate neutrinos, the predicted branching ratio BR$(μ\to e γ)$ strongly depends on $m_ν$ and $U_{e3}$. For $U_{e3}\simeq 0.05$ with $m_ν\simeq 0.3 \eV$, the prediction is close to the present experimental upper bound if the right-handed Majorana neutrino masses are degenerate. On the other hand, the prediction is larger than the experimental upper bound for $U_{e3}\geq 0.05$ in the case of the inverse-hierarchical neutrino masses.
To search for possible textures of lepton mass matrices, we systematically examine flavor mixing structures which can lead to large lepton mixing angles. We find out 37 mixing patterns are consistent with experimental data, taking into account phase factors in the mixing matrices. Only six of the patterns can explain the observed data without any tuning of parameters, while the others need particular choices for the phase values. It is found that these six mixing patterns are those predicted by the models which have been proposed to account for fermion mass hierarchies. On the other hand, the others may give new flavor mixing structures of lepton mass matrices and therefore new possibilities of model construction.
The measurement of the charged-current 8B solar neutrino reaction on deuterium at the Sudbury Neutrino Observatory confirms the neutrino oscillation hypothesis for the solar neutrino problem, and the result favours the solution with large neutrino mixing angles. We demonstrate that the current neutrino oscillation data (including atmospheric and reactor neutrinos) are sufficient to construct the lepton flavour mixing matrix with a reasonable accuracy. We also infer the maximum size of CP violation effects consistent with the current neutrino oscillation experiments.
The predictions of $U_{e3}$ are discussed. Typical models which lead to the large, the seizable and the tiny $U_{e3}$ are also studied.
The search for possible mixing patterns of charged leptons and neutrinos is important to get clues of the origin of nearly maximal mixings, since there are some preferred bases of the lepton mass matrices given by underlying theories. We systematically examine the mixing patterns which could lead to large lepton mixing angles. We find out 37 mixing patterns are consistent with experimental data if taking into account phase factors in the mixing matrices. Only 6 patterns of them can explain the observed data without any tuning of parameters, while the others need particular choices for phase values.
We study the low-energy consequences of the mass and mixing angle relations in grand unified theories (GUT), which follow from an assumption that some quarks and leptons are placed in the same GUT multiplets. This assumption is a simple extension of that for the well-known bottom/tau mass ratio, which is one of the most successful predictions of grand unification of matter multiplets. We show that imposing the GUT relations leads naturally to a limited parameter space from the large lepton mixing between the second and third generations.
We have studied implications of the generic lopsided mass matrix of the charged leptons by taking the SU(5) GUT relation in the nearest-neighbor interaction (NNI) basis. We have found four interesting relations among the lepton mixings and the quark ones, which are independent of details of the model. These relations are discussed by using the experimental data. We have also discussed the relation between U_{e2} and U_{e3} incuding the contribution from the neutrino mass matrix. We have presented the probable value U_{e3}=0.05 \sim 0.16, which is independent of the solar neutrino solutions. The CP violating quantity J_{CP} is also discussed.
We have discussed the quark-lepton mass matrices with the U(1) flavor symmetry in SU(5), which lead to the large mixing angle MSW solution of solar neutrinos. The solar neutrino solution depends on the next-leading terms in the neutrino mass matrix. We have found the lepton mass matrices with the $U(1)\times Z_2$ symmetry, which give the LMA-MSW solution uniquely. The coefficients of the matrix elements of the charged leptons are constrained strongly due to the bound of $U_{e3}$ in the CHOOZ experiment.
It is shown that the bi-maximal solution is the only possibility to reconcile Zee-type neutrino mass matrix with three flavors to the current atmospheric and solar neutrino experimental data. The mass of the lightest neutrino, which consist mostly of $ν_μ$ and $ν_τ$, is $\simeq Δm_{\odot}^2/(2\sqrt{Δm_{atm}^2})$. The related topics on Zee-type neutrino mass matrix are also discussed.
It is well known that Zee type neutrino mass matrix can provide bi-maximal neutrino mixing for three neutrinos. We study the reconciliation of this model with the gauge mediated supersymmetry breaking scenario, which naturally suppresses the large flavor changing neutral current and CP violation in the supersymmetric standard model. When the messenger fields have suitable B-L charges, the radiative correction naturally induces the Zee neutrino mass matrix, which provides tiny neutrino masses and large lepton flavor mixings. Our numerical results are consistent with the neutrino oscillation experiments in both three and four neutrino models.
We impose $O(3)_L\times O(3)_R$ flavor symmetry in the supersymmetric standard model. Three lepton doublets $\ell_i$ transform as an $O(3)_L$ triplet and three charged leptons $\bar e_i$ as an $O(3)_R$ triplet, while Higgs doublets $H$ and $\bar H$ are $O(3)_L\times O(3)_R$ singlets. We discuss a flavor $O(3)_L\times O(3)_R$ breaking mechanism that leads to "successful" phenomenological mass matrices, so-called "democratic" ones, in which the large $\n_μ-\n_τ$ mixing is naturally obtained. Three neutrinos have nearly degenerate masses of order $0.1\eV$ which may be accesible to future double $\b$-decay experiments. We extend our approach to the quark sector and show that it is well consistent with the observed quark mass hierarchies and the CKM matrix elements. However, the large mass of the top quark requires a relatively large coupling. constant.
I review models which present large flavor mixings of the lepton sector based on the gauge theory.
We explore the phenomenological quark-lepton mass matrices, which are devised following the S$_3$ flavour symmetry principle, yet fully consistent with SU(5) gauge models with the Higgs particles of {\bf 5}, {\bf 45} and their conjugates. The model contains 10 free parameters altogether. When 6 parameters are fixed by charge 2/3 quark and charged lepton masses, charge($-$1/3) quark masses and all quark mixing matrix elements are predicted to be close to experiment, leaving some narrow ranges still as freedom. Further specification of 3 more parameters (using, $m_d$, Cabibbo angle and $|V_{cb}|$) suffices to fix the quark mixing matrix nearly completely, and all elements come out to be in accurate agreement with experiment. We obtain the CP violation phase as a prediction.