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Morimitsu Tanimoto

Publications and source records attributed to Morimitsu Tanimoto.

120 records · Page 7Linked to original sources

Neutrino mass matrix with U(2) flavor symmetry and neutrino oscillations

The three neutrino mass matrices in the $SU(5)\times U(2)$ model are studied focusing on the neutrino oscillation experiments. The atmospheric neutrino anomaly could be explained by the large $ν_μ - ν_τ$ oscillation. The long baseline experiments are expected to detect signatures of the neutrino oscillation even if the atmospheric neutrino anomaly is not due to the neutrino oscillation. However, the model cannot solve the solar neutrino deficit while it could be reconciled with the LSND data.

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Prediction on CP Violation in Long Baseline Neutrino Oscillation Experiments

We predict CP violation in the long baseline accelerator experiments taking into consideration the recent LSND data and the atmospheric neutrino data. The estimated upper bound of CP violation is 0.006, which may be observable in the long baseline accelerator experiments. It is found that the upper bound increases to 0.01 if the LSND data is excluded. The matter effect, which is not CP invariant, is found to be very small in the case we consider.

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Spontaneous CP Violation and Higgs Masses in the Next-to-Minimal Supersymmetric Model

We study the possibility of spontaneous CP violation in the next-to-minimal supersymmetric standard model (NMSSM). It is shown that the spontaneous CP violation is induced by the radiative effects of top, stop, bottom and sbottom superfields. The available regions of parameters, which are obtained by imposing the constraints from experiments, are rather narrow. We also obtain strong constraints for light Higgs masses such as m_H \le 36 GeV numerically. Sum of masses of two light neutral Higgs should set around 93 GeV and charged Higgs boson has a rather higher mass larger than 700 GeV.

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Is CP Violation Observable in Long Baseline Neutrino Oscillation Experiments ?

We have studied CP violation originated by the phase of the neutrino mixing matrix in the long baseline neutrino oscillation experiments. The direct measurements of CP violation is the difference of the transition probabilities between CP-conjugate channels. In those experiments, the CP violating effect is not suppressed if the highest neutrino mass scale is taken to be $1\sim 5 \eV$, which is appropriate for the cosmological hot dark matter. Assuming the hierarchy for the neutrino masses, the upper bounds of CP violation have been caluculated for three cases, in which mixings are constrained by the recent short baseline ones. The calculated upper bounds are larger than $10^{-2}$, which will be observable in the long baseline accelerator experiments. The matter effect, which is not CP invariant, has been also estimated in those experiments.

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Is Zee Model The Model of Neutrino Masses?

Zee model leads naturally to two heavy, strongly degenerate and almost maximally mixed neutrinos and to one light neutrino with small mixing. This pattern coincides with the one needed for a solution of the atmospheric neutrino problem by $\n_\m\A \n_τ$ oscillations and for existence of the two component hot dark matter in the Universe. Furthermore, the oscillations $\bar\n_\m\A \bar\n_e$ can be in the range of sensitivity of KARMEN, LSND experiments. Phenomenology of this scenario is considered and possibility to check it in the forthcoming experiments is discussed. Scenario implies large values and inverse flavour hierarchy of the couplings of the Zee boson with fermions: $f_{e τ} \ll f_{μτ} \leq f_{e μ} \sim 0.1$. Main signatures of scenario are: strongly suppressed signal of $\n_\m\A \n_τ$ oscillation in CHORUS and NOMAD experiments, so that positive result from these experiments will rule out the scenario; possibility of observation of $\n_e\A \n_τ$ oscillations by CHORUS and NOMAD; corrections to the muon decay, neutrino-electron scattering at the level of the experimental errors; branching ratio $B(μ\A e γ)$ bigger than $10^{-13}$. The solar neutrino problem can be solved by introduction of additional very light singlet fermion without appreciable changes of the active neutrino pattern.

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The Unitarity Triangle and Quark Mass Matrices on the NNI Basis

We examine the unitarity triangle of the KM matrix by using the general quark mass matrices on the NNI basis. The Fritzsch anzätz is modified by introducing four additional parameters. The KM matrix elements are expressed in terms of quark mass ratios, two phases and four additional parameters. It is found that the vertex of the unitarity triangle is predicted to be almost in the second quadrant on the $ρ-η$ plane as far as $V_{us}\simeq -{\displaystyle \sqrt{\frac{m_d}{m_s}}e^{ip}+ \sqrt{\frac{m_u}{m_c}}e^{iq}}$ is held.

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Structures of Neutrino Flavor Mixing Matrix and Neutrino Oscillations at CHORUS and NOMAD

We have studied structures of the neutrino flavor mixing matrix focusing on the neutrino oscillations at CHORUS and NOMAD as well as the one at LSND(or KARMEN). We have assumed two typical neutrino mass hierarchies $m_3\simeq m_2\gg m_1$ and $m_3\gg m_2\gg m_1({\rm or}\simeq m_1)$. Taking into account the see-saw mechanism of neutrino masses, the reasonable neutrino flavor mixing patterns have been discussed. The observation of the neutrino oscillation at CHORUS and NOMAD presents us the important constraint for the structure of the neutrino flavor mixing matrix. The atomospheric neutrino anomaly has been discussed in relation to the CHORUS and NOMAD experiments.

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See-saw Enhancement of Neutrino Mixing due to the Right-handed Phases

We study the see-saw enhancement mechanism in presence of the right-handed phases of the Dirac neutrino mass matrix and the Majorana mass matrix. The enhancement condition given by Smirnov is modified. We point out that the see-saw enhancement could be obtained due to the right-handed phases even if the Majorana matrix is proportional to the unit matrix. We show a realistic Dirac mass matrix which causes the see-saw enhancement.

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Electric Dipole Moments of Neutron and Electron in Two-Higgs-Doublet Model with Maximal $CP$ violation

We study the electric dipole moments(EDM) of the neutron and the electron in the two-Higgs-doublet model, in the case that $CP$ symmetry is violated maximally in the neutral Higgs sector. We take account of the Weinberg's operator $O_{3g}=GG\t G$ as well as the operator $O_{qg}=\bar qσ\tilde Gq$ for the neutron, and the Barr-Zee diagrams for the electron. It is found that the predicted neutron EDM could be considerably reduced by the destructive contribution of the two Higgs scalars to get the lower value than the experimental bound. As to the electron EDM, the predicted value is smaller in one order than the experimental one.

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Maximal $CP$ violation in the Higgs Sector and its Effect on the $ρ$ Parameter

We study the conditions of maximal $CP$ violation in the neutral Higgs mass matrix of the two Higgs doublet model. We get fixed values of $\tan\b$ and constraints on the Higgs potential parameters. Two neutral Higgs scalars are constrained to be lighter than the charged Higgs scalar and these two Higgs scalars are expected to be almost degenerate due to the smallness of the $h$ parameter, where $h$ is the CP violating coupling constant of the Higgs interaction. The radiative correction of the $ρ$ parameter from the Higgs scalar exchange is rather small and its sign negative for a wide range of Higgs masses. It follows that maximum $CP$ violation in the two Higgs doublet model is safely allowed for the $ρ$ parameter without the custodial symmetry.

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Neutron Electric Dipole Moment in Two Higgs Doublet Model

We study the effect of the "chromo-electric" dipole moment on the electric dipole moment(EDM) of the neutron in the two Higgs doublet model. We systematically investigate the Weinberg's operator $O_{3g}=GG\t G$ and the operator $O_{qg}=\bar qσ\t Gq$, in the cases of $\tan\b\gg 1$, $\tan\b\ll 1$ and $\tan\b\simeq 1$. It is shown that $O_{sg}$ gives the main contribution to the neutron EDM compared to the other operators, and also that the contributions of $O_{ug}$ and $O_{3g}$ cancel out each other. It is pointed out that the inclusion of second lightest neutral Higgs scalar adding to the lightest one is of essential importance to estimate the neutron EDM. The neutron EDM is considerably reduced due to the destructive contribution with each other if the mass difference of the two Higgs scalars is of the order $O(50\G)$.

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Penguin Effects on K Pi and PiPi Decays of the $B$ Meson

We give the detailed analyses for the gluonic-penguin effect on the $\kp$ and $\pp$ decays of the $B$ meson. In the standard model, it is shown that the ratio $BR(B\A\kp)/BR(B\A\pp)$ takes the value $0.5\sim 3.0$ with the strongly depending on the CP violating phase $ϕ$ and the KM matrix element $|V_{ub}|$. We obtain the constraint on the form factor by using the experimental branching ratio. It is also found that, in the two-Higgs-doublet model, the charged Higgs contribution which could enhance the $B\A X_s\r$ decay does not a sizable effect on our processes. The effect of the final state interaction on these processes is also discussed.

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