arXiv subjects

M. Tanimoto

Publications and source records attributed to M. Tanimoto.

45 records · Page 3Linked to original sources

arXiv1999

Zee Mass Matrix and Bi-Maximal Neutrino Mixing

We investigate neutrino masses and mixings within the framework of the Zee mass matrix, with three lepton flavors. It is shown that the bi-maximal solution is the only possibility to reconcile atmospheric and solar neutrino data, within this ansatz. We obtain two almost degenerate neutrinos, which are mixtures of all three neutrino flavors, with heavy masses $\simeq \sqrt{Δm_{atm}^2}$. The predicted mass of the lightest neutrino, which should consist mostly of $ν_μ$ and $ν_τ$, is $\simeq Δm_{\odot}^2/(2\sqrt{Δm_{atm}^2})$.

hep-ph↗

arXiv1998

Embedding Phenomenological Quark-Lepton Mass Matrices into SU(5) Gauge Models

We construct phenomenological quark-lepton mass matrices based on S$_3$ permutation symmetry in a manner fully compatible with SU(5) grand unification. The Higgs particles we need are {\bf 5}, {\bf 45} and their conjugates. The model gives a charge $-$1/3 quark vs charged lepton mass relation, and also a good fit to mass-mixing relations for the quark sector, as well as an attractive mixing pattern for the lepton sector, explaining a large mixing angle between $ν_μ$ and $ν_τ$, and either large or small $ν_e-ν_μ$ mixing angle, depending on the choice of couplings, consistent with the currently accepted solutions to the solar neutrino problem.

hep-ph↗

arXiv1998

Quark Mass Hierarchy, FCNC and CP violation in a Seesaw model

The seesaw model of quark masses is studied systematically, focusing on its developments. A framework allowing the top quark mass to be of the order of the electroweak symmetry breaking scale, while the remaining light quarks have much smaller masses, due to the seesaw mechanism, is presented. The violation of the GIM mechanism is shown to be small and the tree level FCNC are suppressed naturally. In this model, there are many particles which could contribute to the FCNC in the one-loop level. Parameters of the model are constrained by using the experimental data on K^0-\bar{K}^0 mixing and ε_K. The rare K meson decays K_{L,S} -> π^0 ν\barν and K^+ -> π^+ ν\barν are also investigated in the model. In these processes the scalar operators (\bar{s}d)(\barν_τν_τ), which are derived from box diagrams in the model, play an important role due to an enhancement factor M_K/m_s in the matrix element <π|\bar{s}d|K>. It is emphasized that the K_L decay process through the scalar operator is not the CP violating mode, so B(K_L -> π^0 ν\barν) remains non-zero even in the CP conserved limit. The pion energy spectra for these processes are predicted.

hep-ph↗

arXiv1998

Rare Decay of K Meson

We investigate the rare decay processes of the K mesons, K_{L,S} -> π^0 ν\barν and K^{+} -> π^+ ν\barν in LR model with lepton family number being well conserved. In these processes, scalar operators (\bar{s}d)(\barν_τν_τ), which are derived from box diagram in LR model, play an important role due to an enhancement factor M_{K}/m_{s} in the matrix element $<π|\bar{s}d|K>$. It is emphasized that the K_{L} decay process through the scalar operator is not the CP violating mode, so the B(K_L -> π^{0} ν\barν) remains non-zero even in the CP conserved limit. We present the pion energy spectrum for these processes and discuss the effects of LR model.

hep-ph↗

arXiv1998

Atmospheric Neutrino Oscillation and a Phenomenological Lepton Mass Matrix

We propose simple phenomenological lepton mass matrices which describe the three neutrinos almost degenerate in mass, leading to a very large mixing angle between $ν_μ$ and $ν_τ$, as consistent with a recent report on atmospheric neutrino oscillation from the Superkamiokande collaboration. Our matrix model also gives $ν_e-ν_μ$ mixing in agreement with the value required for neutrino oscillation to explain the solar neutrino problem.

hep-ph↗

arXiv1997

The top quark mass and flavor mixing in a Seesaw model of Quark Masses

The top quark mass and the flavor mixing are studied in the context of a Seesaw model of Quark Masses based on the gauge group $SU(2)_L \times SU(2)_R \times U(1)$. Six isosinglet quarks are introduced to give rise to the mass hierarchy of ordinary quarks. In this scheme, we reexamine a mechanism for the generation of the top quark mass. It is shown that, in order to prevent the Seesaw mechanism to act for the top quark, the mass parameter of its isosinglet partner must be much smaller than the breaking scale of $SU(2)_R$. As a result the fourth lightest up quark must have a mass of the order of the breaking scale of $SU(2)_R$, and a large mixing between the right-handed top quark and its singlet partner occurs. We also show that this mechanism is compatible with the mass spectrum of light quarks and their flavor mixing.

hep-ph↗

arXiv1995

Renormalization Effect on Large Neutrino Flavor Mixing in the Minimal Supersymmetric Standard Model

In the minimal supersymmetric standard model, we have studied the evolution of the neutrino flavor mixing by using the renormalization group equation(RGE) with the Georgi-Jarlskog texture for the Yukawa coupling matrices.For the large Yukawa coupling of the charged lepton, i.e.,$\tan\b \gg 1$, the neutrino flavor mixing increases significantly with running down to the electroweak scale by the RGE. If one wishes to get the large neutrino flavor mixing $\sin þ_{23}$ at the electroweak scale, which is suggested by the muon neutrino deficit in the atomospheric neutrino flux, the initial condition $\sin þ_{23}\geq 0.27$ is required at the GUT scale. Combined with the see-saw enhancement of the neutrino flavor mixing, the large mixing is naturally reproduced by setting the reasonable initial condition.

hep-ph↗

arXiv1994

Neutron Electric Dipole Momento in Two-Higgs-Doublet Model

The effect of the "chromo-electric" dipole moment on the electric dipole moment(EDM) of the neutron is studied in the two-Higgs-doublet model. The Weinberg's operator $O_{3g}=GG\t G$ and the operator $O_{qg}=\bar qσ\t Gq$ are both investigated in the cases of $\tan\b\gg 1$, $\tan\b\ll 1$ and $\tan\b\simeq 1$. The neutron EDM is considerably reduced due to the destructive contribution with two light Higgs scalars exchanges.

hep-ph↗

arXiv1994

Penguin-Diagram Induced $B \rightarrow K_Xϕ$ Decays in the Standard Model and in the Two-Higgs-Doublet Model

We systematically analyse the gluonic penguin-induced charmless decays $B \ra K_Xϕ$($K_X$ denotes the meson state $s\bar q \;(q=u\ {\rm or}\ d)$ ), in the standard model and the two-Higgs-doublet model. These processes, being induced at one-loop level, are of great importance in measuring the virtual top quark effect in the standard model, and also in searching for the non-standard signals in the low energy region. It is shown that the QCD effect is also significant in these processes, as in the weak radiative processes $B \ra X_s γ$. We also show that the charged Higgs contribution can not provide sizable enhancements for the decays $B \ra K_Xϕ$, in contrast to the decays $B \ra K_Xγ$. It is also found that processes such as $B \ra K_1(1400)ϕ$ and $B \ra K(1460)ϕ$ have large branching fractions among $B \ra K_Xϕ$ decays.

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