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Hiroyuki Nishiura

Publications and source records attributed to Hiroyuki Nishiura.

At least 37 records · Page 2Linked to original sources
arXiv2011

Unified description of quark and lepton mixing matrices based on a Yukawaon model

Based on a supersymmetric Yukawaon model with O(3) family symmetry, possible forms of quark and lepton mixing matrices are systematically investigated under a condition that the up-quark mass matrix form leads to the observed nearly tribimaximal mixing in the lepton sector. Although the previous model could not provide a good fitting of the observed quark mixing, the present model can give a reasonably good fitting not for lepton mixing but also the quark mixing by using a different origin of the $CP$ violation from one in the previous model.

hep-ph↗
arXiv2010

Universal Mass Matrix and Leptonic $θ_{13}$ Angle

We propose a universal mixing hypothesis between quark and lepton sectors at high energy scale (probably GUT scale) where quark-lepton universality holds. Namely in the charged lepton diagonal base, all the other mass matrices for up and down quarks and neutrinos are diagonalized by the same unitary matrix except for the phase elements. Thanks to this hypothesis, the observed values of the Cabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix and the mixing angles $θ_{12}$ and $θ_{23}$ in the Maki-Nakagawa-Sakata (MNS) lepton mixing matrix can predict the unknown magnitudes of the mixing angle $θ_{13}$ and of the CP violating Dirac phase $δ$ in the MNS matrix. Their allowed regions are rather narrow, $0.036<{sin}θ_{13}<0.048$ and $6^\circ<δ<12^\circ$.

hep-ph↗
arXiv2009

New Parameterization in Muon Decay and the Type of Emitted Neutrino. II

In a previous paper, new sets of parameters to replace the Michel parameters were proposed to analyze data for the muon decay $μ^{+} \to e^{+}ν_{e}\bar{ν_μ}$. Both $(V-A)$ and $(V+A)$ charged currents with finite neutrino mass have been used to study this decay. In the present paper, this parameterization is extended to a more general form, and a method for data analysis (least squares) is discussed for the propose of determining the rate of contribution from the $(V+A)$ current. We find that there is a simple form in which the set of parameters is related primitively to the physical quantities. It is shown that the Michel parameters are one of the other sets that are obtained from this simple form by rearranging one term. We derive the condition to obtain the same information regarding unknown physical quantities in the case that the data are analyzed using these simple and rearranged forms separately. We find that there is some possibility to get different results from these analyses, because the equivalent condition is very delicate and the QED radiative corrections should be treated carefully. We propose a consistent formula for data analysis. It is useful to compare the value obtained in the least squares fit using the simple form with that obtained using the prediction of the standard model, because a large difference is not expected, especially in the case of the Majorana neutrino. Finally, we point out that the method we proposed to determine the type of neutrino in the previous paper is incorrect.

hep-ph↗
arXiv2009

Maximal CP Violation Hypothesis and a Lepton Mixing Matrix

Maximal CP violation hypothesis is applied to a simple lepton mixing matrix form U=V_{CKM}^\dagger U_{TB}, which has recently been speculated under an ansatz that U becomes an exact tribimaximal mixing U_{TB} in a limit of the quark mixing matrix V_{CKM} \to {\bf 1}. The prediction \tan^2 θ_{12} =1/2 in the case of the exact tribimaximal mixing U=U_{TB} is onsiderably spoiled in the speculated mixing U=V_{CKM}^\dagger U_{TB}. However, the application of the hypothesis to the lepton sector can again recover the spoiled value to \tan^2 θ_{12} \simeq 1/2 if the original Kobayashi-Maskawa phase convention for V_{CKM} is adopted.

hep-ph↗
arXiv2008

Quark Mixing from Mass Matrix Model with Flavor 2 (\leftrightarrow) 3 Symmetry

We consider an universal mass matrix model which has a seesaw-invariant structure with the most general texture based on flavor 2 (\leftrightarrow) 3 symmetry common to all quarks and leptons. The CKM quark mixing matrix of the model is analyzed. It is shown that the model is consistent with all the experimental data of quark mixings by tuning free parameters of the model. We also show that the values of parameters of the present model consistent with the experimental data are not far from the ones of the mass matrix model with a vanishing (1,1) element.

hep-ph↗
arXiv2008

Testable Deviation from Exact Tribimaximal Mixing

A simple relation U_{MNS}=V_{CKM}^\dagger U_{TB} between the lepton and quark mixing matrices (U_{MNS} and V_{CKM}) is speculated under an ansatz that U_{MNS} becomes an exact tribimaximal mixing U_{TB} in a limit V_{CKM}={\bf 1}. By using the observed CKM mixing parameters, possible values of neutrino oscillation parameters are estimated: \sin^2 θ_{13}=0.024-0.028, \sin^2 2θ_{23}=0.94-0.95 and \tan^2 θ_{12}=0.24-1.00 depending on phase conventions of U_{TB}. Those values are testable soon by precision measurements in neutrino oscillation experiments.

hep-ph↗
arXiv2007

Zero Texture Model and SO(10) GUT

We study the bridge between the phenomenological mass matrix model and SO(10) GUT. Namely, we consider the four zero texture model in the framework of the renormalizable SO(10) GUT model. This unification gives more stringent constraints than the case where only either model is considered. However, we can obtain good fitting by expanding the minimal SO(10) GUT to include 120 in addition to 10 and \bar 126 in Yukawa coupling and by considering both type-I and type-II seesaw mechanisms.

hep-ph↗
arXiv2006

Can four-zero-texture mass matrix model reproduce the observed quark and lepton mixing angles and CP violating phases?

We reconsider an universal mass matrix model which has a seesaw-invariant structure with four-zero texture common to all quarks and leptons. The CKM quark and MNS lepton mixing matrices of the model are analyzed analytically.We show that the model can be consistent with all the experimental data of neutrino oscillation and quark mixings by tuning free parameters of the model. It is also shown that the model predicts a relatively large value for (1,3) element of the MNS lepton mixing matrix, |(U_{MNS})_{13}|^2 \simeq 2.6 \times 10^{-2}. Using the seesaw mechanism, we also discuss the conditions for the components of the Dirac and the right-handed Majorana neutrino mass matrices which lead to the neutrino mass matrix consistent with the experimental data.

hep-ph↗
arXiv2006

Majorana Neutrinos in Muon Decay

The normal muon decay $μ^{+} \to e^{+}ν_{e}\bar{ν_μ}$ is studied as a tool to discriminate between the Dirac and Majorana type neutrinos. For the purpose to do this, we propose a new parameterization in place of the Michel parameters for the energy spectrum of $e^{+}$. The $χ^2$-fitting is used by noticing different energy spectra between the Dirac and Majorana neutrino cases. We assume the interaction Hamiltonian which consists of the $V-A$ and $V+A$ charged currents.

hep-ph↗
arXiv2005

Broken Flavor 2 <-> 3 Symmetry and phenomenological approach for universal quark and lepton mass matrices

A phenomenological approach for the universal mass matrix model with a broken flavor 2 <-> 3 symmetry is explored by introducing the 2 <-> 3 antisymmetric parts of mass matrices for quarks and charged leptons . We present explicit texture components of the matrices, which are consistent with all the neutrino oscillation experiments and quark mixing data. The mass matrices have a common structure for quarks and leptons, while the large lepton mixings and the small quark mixings are derived with no fine tuning due to the difference of the phase factors. The model predicts a value, 2.4 x 10^{-3}, for the lepton mixing matrix element square |U_{13}|^2, and also predict =(0.89-1.4) x 10^{-4} eV for the averaged neutrino mass which appears in the neutrinoless double beta decay.

hep-ph↗
arXiv2005

New Parameterization in Muon Decay and the Type of Emitted Neutrino

Normal muon decay, $μ^{+} \to e^{+}ν_{e}\bar{ν_μ}$, is studied as a tool to discriminate between the Dirac and Majorana types of neutrinos and to survey the structure of the weak interaction. It is assumed that massive neutrinos mix with one another and that the interaction Hamiltonian consists of the $V-A$ and $V+A$ charged currents. A new set of parameters used in place of the Michel parameters is proposed for the positron distribution. Explicit forms of these new parameters are obtained by assuming that the masses are less than 10 eV for light neutrinos and sufficiently large for heavy Majorana neutrinos, which are not emitted in the muon decay. It is shown that a possible method to discriminate between the Dirac and Majorana cases is to use a characterization given by the $χ^2$ fitting of their spectra. It is also confirmed that the theoretical predictions in the Majorana neutrino case are almost the same as those obtained from the standard model. Indeed, their differences cannot be distinguished within the present experimental precision.

hep-ph↗
arXiv2005

Large Lepton Mixing and Nonsymmetric Mass Matrices with Flavor 2 <-> 3 Symmetry

We analyze the lepton sector of a recently proposed nonsymmetric mass matrix model. Our model gives a unified description of quark and lepton with the same texture form based on an extended flavor $2 \leftrightarrow 3$ symmetry with a phase. By investigating possible types of assignment for masses, we find that the model can lead to large lepton mixings which are consistent with experimental values. We also find that the model predicts a very small value, $1.3\times10^{-10}$, for the lepton mixing matrix element square $|U_{13}|^2$. The CP violating phases in the lepton mixing matrix and a suppression of the averaged neutrino mass in the neutrinoless double beta decay are also predicted.

hep-ph↗
arXiv2005

Prediction for Quark Mixing from Universal Quark and Lepton Mass Matrices with Flavor 2 <-> 3 Symmetry

We propose a mass matrix model that gives a unified description of quark and lepton with the same texture form based on a flavor 2 <-> 3 symmetry. The model is in contrast with the conventional picture that the mass matrix forms in the quark sector will take somewhat different structures from those in the lepton sector. By investigating possible types of assignment for masses, we find that our quark mass matrices can lead to small CKM quark mixings which are consistent with experimental values. We also find some phase-parameter-independent relations among CKM quark mixing matrix elements.

hep-ph↗
arXiv2004

Lepton Mixing Matrix Element U_{13} and New Assignments of Universal Texture for Quark and Lepton Mass Matrices

We reanalyze the mass matrix model of quarks and leptons that gives a unified description of quark and lepton mass matrices with the same texture form. By investigating possible types of assignment for the texture components of the lepton mass matrix, we find that a different assignment for neutrinos than for charged leptons can also lead to consistent values of the MNSP lepton mixing matrix. We also find that the predicted value for the lepton mixing matrix element $U_{13}$ of the model depends on the assignment. A proper assignment will be discriminated by future experimental data for $U_{13}$.

hep-ph↗
arXiv2003

Assignments of Universal Texture Components for Quark and Lepton Mass Matrices

We reanalyze the mass matrices model of quarks and leptons which gives a unified description of quark and lepton mass matrices with the same texture form. By investigating possible types of the assignment for the texture's components of this mass matrix form, we find that a different assignment for up-quarks from one for down-quarks can lead to consistent values of CKM mixing matrix. This finding overcomes a weak point of the previous analysis of the model. We also obtain some relations among the CKM mixing matrix parameters, which are independent of evolution effects.

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