To be published Physical Review D.
Evolution of the Yukawa coupling constans and seesaw
operators in the universal seesaw model
Yoshio Koide and Hideo Fusaoka
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 $\tan\beta$ (in the SUSY model).
Can the SO(10) Model with Two Higgs Doublets Reproduce the Observed Fermion Masses?
K.Matsuda, Y.Koide, T.Fukuyama
It is usually considered that the SO(10) model with one 10 and one 126 Higgs scalars cannot reproduce the observed quark and charged lepton masses. Against this conventional conjecture, we find solutions of the parameters which can give the observed fermion mass spectra. The SO(10) model with one 10 and one 120 Higgs scalars is also discussed.
Physical Review D63, 037301 (2001).
Bimaximal Neutrino Mixing in a Zee-type Model with Badly Broken Flavor Symmetry
Yoshio Koide and Ambar Ghosal
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 $\Delta m^2_{solar}/\Delta m^2_{atm} \simeq \sqrt{2} m_e/m_{\mu}=6.7 \times 10^{-3}$, which are in excellent agreement with the observed data. In the near future, the lepton-number violating decay $Z\to \mu^\pm \tau^\mp$ will be observed
To be published in the Proceedings of
the workshop on "Neutrino Oscillations and their Origin",
at Fuji-Yoshida, Feb., 2000,
Universal Academy Press, Tokyo, 2000
Large Angle Neutrino Mixing and Pseudo-Dirac Neutrinos
A possibility that the observed large angle neutrino mixing is
caused by a set of pseudo-Dirac neutrinos is discussed.
Since the recent Superkamiokande data disfavor to the large
$\nu_\mu$-$\nu_s$ mixing, a model without a large
$\nu_\mu$-$\nu_s$ mixing is also discussed.
Phys.Lett. B488 (2000) 344-350
.
Democratic Universal Seesaw Model with Three Light Sterile Neutrinos
Yoshio Koide and Ambar Ghosal
Based on the ``democratic" universal seesaw model,
where mass matrices $M_f$ of quarks and leptons f_i
(f=u,d,\nu,e; i=1,2,3) are given by a seesaw form
M_f\simeq -m_L M_F^{-1} m_R, and m_L and m_R are universal
for all the fermion sectors, and the mass matrices M_F of
hypothetical heavy fermions F_i have a democratic structure,
a possible neutrino mass matrix is investigated.
In the model, there are three sterile neutrinos \nu_{iR}
which mix with the active neutrinos \nu_{iL} with
\theta \sim 10^{-2} and which are harmless for cosmological
constraints. The atmospheric, solar and LSND neutrino data
are explained by the mixings \nu_{\mu L} \leftrightarrow
\nu_{\tau L}, \nu_{eL} \leftrightarrow \nu_{eR} and
\nu_{eL} \leftrightarrow \nu_{\mu L}, respectively.
The model predicts that \Delta m^2_{solar}/\Delta m^2_{atm}
\simeq m_e/\sqrt{m_{\mu} m_{\tau}} and \Delta m_{LSND}^2/
\Delta m^2_{atm} \simeq (1/4)\sqrt{m_{\mu}/m_e}
(\Delta m^2_{solar} \simeq 3\times 10^{-6} eV^2 and
\Delta m_{LSND}^2 \simeq 0.5 eV^2 for \Delta} m^2_{atm}
\simeq 2.2\times 10^{-3} eV^2), and \sin^{2}2\theta_{atm}
\simeq 1 and \sin^{2} 2\theta_{LSND} \simeq 4m_e/m_{\mu}
\simeq 0.02.
Quark and Lepton Mass Matrices with a Cyclic Permutation Invariant Form
As an attempt to give an unified description of quark and lepton mass
matrices M_f, the following mass matrix form is proposed: the form of
the mass matrices are invariant under a cyclic permutation
(f_1 \rightarrow f_2, f_2 \rightarrow f_3, f_3 \rightarrow f_1)
among the fermions f_i. The model naturally leads to the maximal mixing
between \nu_\mu and \nu_\tau, and with an additional ansatz, it leads to
the well-satisfied relations |V_{us}| \simeq \sqrt{m_d/m_s} and |V_{cb}|
\simeq \sqrt{m_d/m_b}.
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A Two Parameter Texture of Nearly Bi-maximal Neutrino Mixing
We propose a texture of three generation Majorana-type neutrino mass matrix
in terms of only two parameters which gives rise to nearly bi-maximal mixing
angles. We also demonstrate an explicit realization of such type of neutrino
mass-matrix in the context of an $SU(2)_L$$\times$$U(1)_Y$ model due to
higher dimensional mass terms through the inclusion of discrete
$Z_3$$\times$$Z_4$ symmetry and two extra singlet Higgs fields.
An Exact Solution of the Randall-Sundrum Model and the Mass Hierarchy Problem
An exact solution of the Randall-Sundrum model for a simplified case
(one wall) is obtained. It is given by the $1/k^2$-expansion (thin wall
expansion) where $1/k$ is the thickness of the domain wall. The vacuum
setting is done by the 5D Higgs potential and the solution is for a family
of the Higgs parameters. The mass hierarchy problem is examined.
Some physical quantities in 4D world such as the Planck mass,
the cosmological constant, and fermion masses are focussed.
Similarity to the domain wall regularization used in the chiral
fermion problem is pointed out. We propose and examine the possibility
that the 4D massless chiral fermion bound to the domain wall in the
5D world can be regarded as the real 4D fermions such as neutrinos,
quarks and other leptons.