arXiv subjects

Yoshio Koide

Publications and source records attributed to Yoshio Koide.

At least 91 records · Page 5Linked to original sources

arXiv2004

Neutrino Masses Without Seesaw Mechanism in a SUSY SU(5) Model With Additional $\bar{5}'_L+5'_L$

A radiatively-induced neutrino mass matrix with a simple structure is proposed on the basis of an SU(5) SUSY GUT model with R-parity violation. The model has matter fields $\bar{5}'_{L}+5'_{L}$ in addition to the ordinary matter fields $\bar{5}_{L}+10_{L}$ and Higgs fields $H_u+\bar{H}_d$. The R-parity violating terms are given by $\bar{5}_{L} \bar{5}_{L} 10_{L}$, while the Yukawa interactions are given by $\bar{H}_d \bar{5}'_{L} 10_{L}$. Since the matter fields $\bar{5}'_L$ and $\bar{5}_L$ are different from each other at the unification scale, the R-parity violation effects at a low energy scale appear only through the $\bar{5}'_L \leftrightarrow \bar{5}_{L}$ mixings. In order to make this R-parity violation effect harmless for proton decay, a discrete symmetry Z_3 and a triplet-doublet splitting mechanism analogous to the Higgs sector are assumed.

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arXiv2004

What Happens If an Unbroken Flavor Symmetry Exists?

Without assuming any specific flavor symmetry and/or any specific mass matrix forms, it is demonstrated that if a flavor symmetry (a discrete symmetry, a U(1) symmetry, and so on) exists, we cannot obtain the CKM quark mixing matrix $V$ and the MNS lepton mixing matrix $U$ except for those between two families for the case with the completely undegenerated fermion masses, so that we can never give the observed CKM and MNS mixings. Only in the limit of $m_{ν1} =m_{ν2}$ ($m_d=m_s$), we can obtain three family mixing with an interesting constraint $U_{e3}=0$ ($V_{ub}=0$).

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arXiv2004

Comments on a Flavor Symmetry

It is pointed out that if a flavor symmetry (a discrete symmetry, a U(1) symmetry, and so on) exists, we cannot obtain the observed CKM quark mixing matrix V_q and MNS lepton mixing matrix U_\ell, even if we can obtain reasonable mass spectra under the symmetry. Such the serious constraint is derived only from the SU(2)_L conditions, and we will not assume any explicit flavor symmetry and/or any explicit mass matrix forms. And then, we will discuss the meaning of the severe constraint.

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arXiv2004

Neutrino Masses Induced by R-Parity Violation in a SUSY SU(5) Model with Additional \bar{5}'_L+5'_L

Within the framework of an SU(5) SUSY GUT model, a possible general form of the neutrino mass matrix induced by R-parity violation is investigated. The model has matter fields \bar{5}'_{L}+5'_{L} in addition to the ordinary matter fields \bar{5}_{L}+10_{L} and Higgs fields H_u+\bar{H}_d. The R-parity violating terms are given by \bar{5}_{L} \bar{5}_{L} 10_{L}, while the Yukawa interactions are given by \bar{H}_d \bar{5}'_{L} 10_{L}. Since the matter fields \bar{5}'_L and \bar{5}_L are different from each other at the unification scale, the R-parity violation effects at a low energy scale appear only through the \bar{5}'_L \leftrightarrow \bar{5}_{L} mixings. In order to make this R-parity violation effect harmless for proton decay, a discrete symmetry Z_3 and a triplet-doublet splitting mechanism analogous to that in the 5-plet Higgs fields are assumed.

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arXiv2004

Universal Texture of Quark and Lepton Mass Matrices with an Extended Flavor $2\leftrightarrow 3$ Symmetry

Against the conventional picture that the mass matrix forms in the quark sectors will take somewhat different structures from those in the lepton sectors, on the basis of an idea that all the mass matrices of quarks and leptons have the same texture, a universal texture of quark and lepton mass matrices is proposed by assuming a discrete symmetry Z_3 and an extended flavor 2\leftrightarrow 3 symmetry. The texture is described by three parameters (including phase parameter). According to this ansatz, the neutrino masses and mixings are investigated.

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arXiv2003

Radiative Neutrino Masses in a SUSY GUT Model

Radiatively-induced neutrino mass matrix is investigated within the framework of an SU(5) SUSY GUT model. The model has matter fields of three families \bar{5}_{L(+)i}+5_{L(+)i} in addition to the ordinary matter fields \bar{5}_{L(-)i}+10_{L(+)i} and Higgs fields H_{(+)}+\bar{H}_{(0)}, where (+,0,-) denote the transformation properties (ω^{+1},ω^0,ω^{-1}) (ω^3=+1) under a discrete symmetry Z_3. R-parity violating terms are given by \bar{5}_{L(+)} \bar{5}_{L(+)} 10_{L(+)}, while the Yukawa interactions are given by \bar{H}_{(0)} \bar{5}_{L(-)} 10_{L(+)}, i.e. the \bar{5}-fields in both are different from each other. The Z_3 symmetry is only broken by the terms \bar{5}_{L(+)i}5_{L(+)i} softly, so that the \bar{5}_{L(+)i}\leftrightarrow \bar{5}_{L(-)i} mixings appear at μ< M_X. Of the R-parity violating terms \bar{5}_{L(+)} \bar{5}_{L(+)} 10_{L(+)}, only the terms (e_Lν_-ν_Le_)e_R^c sizably appear at μ< M_X.

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arXiv2003

R-Parity Violation in a SUSY GUT Model and Radiative Neutrino Masses

Within the framework of an SU(5) SUSY GUT model, a mechanism which effectively induces R-parity-violating terms below the unification energy scale M_X is proposed. The model has matter fields \bar{5}_{L(+)}+10_{L(-)} and Higgs fields H_{(-)} and \bar{H}_{(+)} in addition to the ordinary Higgs fields H_{(+)} and \bar{H}_{(-)} which contribute to the Yukawa interactions, where (\pm) denote the transformation properties under a discrete symmetry Z_2. The Z_2 symmetry is only broken by the μ-term \bar{H}_{(+)}H_{(-)} softly, so that the \bar{5}_{(+)}\leftrightarrow \bar{H}_{(+)} \leftrightarrow \bar{H}_{(-)} mixing appears at μ< m_{SB}, i.e. R-parity violating terms \bar{5}_L\bar{5}_L 10_L are effectively induced from the Yukawa interactions \bar{H}_{(-)}\bar{5}_{L(+)}10_{L(-)}, so that the effective coupling constants λ_{ijk} of ν_{Li} e_{Lj} e_{Rk}^c and ν_{Li} d_{Rj}^c d_{Lk} are proportional to the mass matrices (M_e^*)_{jk} and (M_d^\dagger)_{jk}, respectively. The parameter regions which are harmless for the proton decay are investigated. Possible forms of the radiatively induced neutrino mass matrix are also investigated.

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arXiv2003

Universal Texture of Quark and Lepton Mass Matrices

Against the conventional picture that the mass matrix forms in the quark sectors will take somewhat different structures from those in the lepton sectors, a possibility that all the mass matrices of quarks and leptons have the same form as in the neutrinos is investigated. For the lepton sectors, the model leads to a nearly bimaximal mixing with the prediction |U_{e3}|^2=m_e/2m_μ=0.0024 and \tan^2θ_{sol} \simeq m_{ν1}/m_{ν2}, and so on. For the quark sectors, it can lead to reasonable values of the CKM mixing matrix and masses: |V_{us}|\simeq \sqrt{m_d/m_s}, |V_{ub}| \simeq |V_{cb}|\sqrt{m_u/m_c}, |V_{td}| \simeq |V_{cb}|\cdot |V_{us}|, and so on.

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arXiv2002

An SU(5) SUSY Model with R-Parity Violation and Radiatively Induced Neutrino Masses

The radiatively induced neutrino mass matrix is investigated on the basis of an SU(5) SUSY model. In order to evade the proton decay, an ansatz based on a discrete symmetry $Z_2$ is assumed: although, at the unification scale, we have two types of superfields $Ψ_{L(\pm)}=\bar{5}_{L(\pm)}+10_{L(\pm)}$, which are transformed as $Ψ_{L(\pm)} \to \pm Ψ_{L(\pm)}$ under the discrete symmetry Z$_2$, the particles $Ψ_{L(+)}$ are decoupled after the SU(5) symmetry is broken, so that our quarks and leptons belong to Ψ_{L(-)}. The R-parity-violating terms for our quarks and leptons Ψ_{L(-)} are basically forbidden under the symmetry Z_2. However, we assume that mixings between members of Ψ_{L(+)} and those of Ψ_{L(-)} are in part caused after SU(5) is broken. As a result, the R-parity-violating interactions are in part allowed, so that the neutrino masses are radiatively generated, while the proton decay due to the R-parity violating terms is still forbidden because the term d_R^c d_R^c u_R^c has z=-1.

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arXiv2002

Universal Texture of Quark and Lepton Mass Matrices and a Discrete Symmetry Z_3

Recent neutrino data have been favourable to a nearly bimaximal mixing, which suggests a simple form of the neutrino mass matrix. Stimulated by this matrix form, a possibility that all the mass matrices of quarks and leptons have the same form as in the neutrinos is investigated. The mass matrix form is constrained by a discrete symmetry Z_3 and a permutation symmetry S_2. The model, of course, leads to a nearly bimaximal mixing for the lepton sectors, while, for the quark sectors, it can lead to reasonable values of the CKM mixing matrix and masses.

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arXiv2002

A Unified Description of Quark and Lepton Mass Matrices in a Universal Seesaw Model

In the democratic universal seesaw model, the mass matrices are given by \bar{f}_L m_L F_R + \bar{F}_L m_R f_R + \bar{F}_L M_F F_R (f: quarks and leptons; F: hypothetical heavy fermions), m_L and m_R are universal for up- and down-fermions, and M_F has a structure ({\bf 1}+ b_f X) (b_f is a flavour-dependent parameter, and X is a democratic matrix). The model can successfully explain the quark masses and CKM mixing parameters in terms of the charged lepton masses by adjusting only one parameter, b_f. However, so far, the model has not been able to give the observed bimaximal mixing for the neutrino sector. In the present paper, we consider that M_F in the quark sectors are still "fully" democratic, while M_F in the lepton sectors are partially democratic. Then, the revised model can reasonably give a nearly bimaximal mixing without spoiling the previous success in the quark sectors.

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arXiv2002

Radiatively Induced Neutrino Mass Matrix in a SUSY GUT Model with R-Parity Violation

In order to evade the proton decay which appears when the Zee model is embedded into a SUSY GUT scenario with R-parity violation, a new idea based on a discrete Z_2 symmetry is proposed. Under the symmetry Z_2, the quark and lepton mass matrices are tightly constrained. The admissible form of the radiatively-induced neutrino mass matrix is investigated.

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arXiv2002

Prospect of the Zee model

The Zee model is one of promising models of neutrino mass generation mechanism. However, the original Zee model is not on the framework of the ground unification scenario, and moreover, it is recently pointed out that the predicted value of $\sin^2 2θ_{solar}$ must be satisfied the relation $\sin^2 2θ_{solar} > 0.99$. We discuss whether possible GUT versions of the Zee model can be free from the severe constraint $\sin^2 2θ_{solar} >0.99$ or not. We will conclude that the following two models are promising: an R-parity violating SUSY GUT model and an SO(10) model with a 126-plet scalar.

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arXiv2001

New Trends in the Zee Model

Recent trends in the Zee model are reviewed. Especially, the importance of a serious constraint in the Zee model, sin^2 2θ_{solar} =1.0, is pointed out.

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arXiv2001

Can the Zee Model Explain the Observed Neutrino Data?

The eigenvalues and mixing angles in the Zee model are investigated parameter-independently. When we require |Δm^2_{12}/Δm^2_{23}| \ll 1 in order to understand the solar and atmospheric data simultaneously, the only solution is one which gives bi-maximal mixing. It is pointed out that the observed values \sin^2 2θ_{solar} \simeq 0.66 in the MSW LMA solution cannot be explained within the framework of the Zee model, because we derive a severe constraint on the value of \sin^2 2 θ_{solar}, \sin^2 2 θ_{solar} \geq 1 -(1/16)(Δm^2_{solar}/Δm^2_{atm})^2.

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arXiv2001

Lepton Flavor Violating Z Decays in the Zee Model

We calculate lepton flavor violating (LFV) Z decays Z \to {e_i^\pm}e_j^\mp (i, j = e, μ, τ; i\neq j) in the Zee model keeping in view the radiative leptonic decays e_i\to e_jγ(i = μ, τ; j = e, μ; i\neq j), μdecay and anomalous muon magnetic moment (μAMM). We investigate three different cases of Zee f_{ij} coupling (A) f_{eμ}^2 = f_{μτ}^2= f_{τe}^2, (B) f_{eμ}^2 \gg f_{τe}^2 \gg f_{μτ}^2, and (C) f_{μτ}^2 \gg f_{eμ}^2 \gg f_{τe}^2 subject to the neutrino phenomenology. Interestingly, we find that, although the case (C) satisfies the large excess value of μAMM, however, it is unable to explain the solar neutrino experimental result, whereas the case (B) satisfies the bi-maximal neutrino mixing scenario, but confronts with the result of μAMM experiment. We also find that among all the three cases, only the case (C) gives rise to largest contribution to the ratio B(Z\to e^\pmτ^\mp)/B(Z\to μ^\pm μ^\mp) \simeq {10}^{-8} which is still two order less than the accessible value to be probed by the future linear colliders, whereas for the other two cases, this ratio is too low to be observed even in the near future for all possible LFV Z decay modes.

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arXiv2001

Evolution of the Yukawa coupling constants and seesaw operators in the universal seesaw model

The general features of the evolution of the Yukawa coupling constants and seesaw operators in the universal seesaw model with det M_F=0 are investigated. Especially, it is checked whether the model causes bursts of Yukawa coupling constants, because in the model not only the magnitude of the Yukawa coupling constant (Y_L^u)_{33} in the up-quark sector but also that of (Y_L^d)_{33} in the down-quark sector is of the order of one, i.e., (Y_L^u)_{33} \sim (Y_L^d)_{33} \sim 1. The requirement that the model should be calculable perturbatively puts some constraints on the values of the intermediate mass scales and tanβ(in the SUSY model).

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arXiv2000

Bimaximal Neutrino Mixing in a Zee-type Model with Badly Broken Flavor Symmetry

A Zee-type neutrino mass matrix model with a badly broken horizontal symmetry SU(3)_H is investigated. By putting a simple ansatz on the symmetry breaking effects of SU(3)_H for transition matrix elements, it is demonstrated that the model can give a nearly bimaximal neutrino mixing with the ratio $Δm^2_{solar}/Δm^2_{atm} \simeq \sqrt{2} m_e/m_μ=6.7 \times 10^{-3}$, which are in excellent agreement with the observed data. In the near future, the lepton-number violating decay $Z\to μ^\pm τ^\mp$ will be observed.

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