How Far Can the SO(10) Two Higgs Model
Describe the Observed Neutrino Masses and Mixings ?
K.Matsuda, Y.Koide, T.Fukuyama,
and H. Nishiura
Can the SO(10) model with one {\bf 10} and one {\bf 126} Higgs scalars
give the observed masses and mixings of quarks and leptons without
any other additional Higgs scalars?
Recently, at least, for quarks and charged leptons, it has been
demonstrated that it is possible. However, for the neutrinos,
it is usually said that parameters which are determined from the quark
and charged lepton masses cannot give the observed large neutrino
mixings. This problem is systematically investigated, and it is
concluded that the present data cannot exclude SO(10) model with
two Higgs scalars although it cannot give the best fit values
of the data.
Physical Review D64, 077301 (2001)
M
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
|\Delta m^2_{12}/\Delta m^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 present best-fit value of
\sin^2 2\theta_{solar} 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 \theta_{solar}, \sin^2 2 \theta_{solar} \geq
1 -(1/16)(\Delta m^2_{solar}/\Delta m^2_{atm})^2.
Physical Review D64, 053014
Lepton Flavor Violating $Z$ Decays in the Zee Model
Ambar Ghosal, Yoshio Koide and Hideo Fusaoka
We calculate lepton flavor violating (LFV) Z decays
Z\rightarrow e_i^\pm e_j^\mp (i, j = e, \mu, \tau ; i \neq j)
in the Zee model keeping in view the radiative leptonic decays
e_i\rightarrow e_j \gamma (i = \mu, \tau; j = e, \mu ;
i\neq j), \mu decay and anomalous muon magnetic moment (\mu AMM).
We investigate three different cases of Zee f_{ij} coupling
(A) f_{e\mu}^2 = f_{\mu\tau}^2 = f_{\tau e}^2,
(B) f_{e\mu}^2 \gg f_{\tau e}^2 \gg f_{\mu\tau}^2, and
(C) f_{\mu\tau}^2 \gg f_{e\mu}^2 \gg f_{\tau e}^2 subject
to the neutrino phenomenology. Interestingly, we find that, although
the case (C) satisfies the large excess value of \mu AMM, 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 \mu AMM experiment.
We also find that among all the three cases, only the case (C)
gives rise to largest contribution to the ratio B(Z\rightarrow
e^\pm \tau^\mp)/B(Z\rightarrow \mu^\pm \mu^\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.