arXiv subjects

Masako Bando

Publications and source records attributed to Masako Bando.

At least 37 records · Page 2Linked to original sources

arXiv2002

Neutrino Mass Matrix Out of Up-Quark Masses Only

Under the assumption of symmetric four zero texture for fermion mass matrices in SO(10) model, the neutrino Dirc mass matrix is derived from the up-quark mass matrix. By adjusting two scales of the Majorana mass sector, we can derive observed neutrino two large mixing angles very naturally. It is indeed remarkable that all the masses and mixings of neutrinos are expressed in terms of only three known parameters, $m_t,m_c,m_u$. A typical example of our model is \tan^2 2θ_{τμ}=\frac{4}{(1-2\frac{m_c}{\sqrt{m_u m_t}})^2}.

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arXiv2002

Higgs Doublets as Pseudo Nambu-Goldstone Bosons in Supersymmetric E_6 Unification

The idea to have Higgs doublets as pseudo Nambu-Goldstone (PsNG) multiplet is examined in the framework of supersymmetric E_6 unified theory. We show that extra PsNG multiplets other than the expected Higgs doublets necessarily appear in the E_6 case. If we demand that the extra PsNG multiplets neither disturb the gauge coupling unification nor make the color gauge coupling diverge before unification occurs, only possibility for the extra PsNG is 10+\bar{10} of SU(5). This is realized when the symmetry breaking E_6 \to SO(10) occurs in the ϕ(27)+ϕ(\bar{27}) sector while E_6 \to SU(4)_C\times SU(2)_L\times U(1)\times U(1) in the Σ(78) sector. The existence of 10+\bar{10} multiplets with mass around 1 TeV is therefore a prediction of this E_6 PsNG scenario. Implication of their existence on the proton decay is also discussed.

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arXiv2001

E_6 Unification with Bi-Large Neutrino Mixing

A scenario of SO(10) grand unified theory (GUT) proposed by one of the authors is extended to E_6 unification. This gives realistic quark and lepton mass matrices. In neutrino sector, the model reproduces large mixing angle (LMA) MSW solution as well as large mixing angle for atmospheric neutrino anomaly. In this model, right-handed down quark and left-handed lepton of the first and second generation belong to a single multiplet 27. This causes natural suppression of flavor changing neutral current(FCNC).

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arXiv2001

Brane Fluctuation and New Counting Rules for Kaluza-Klein Towers

In models with extra dimensions, branes have been usually treated as solid bodies though they are prohibited by the relativity. In the previous letter, we proposed a method of taking account of brane fluctuation by introducing Nambu-Goldstone bosons, and prove that when a tension of the brane is small, the interaction between boundary fields and Kaluza-Klein modes is suppressed exponentially. In this letter, we further investigate this suppression in more generic configuration, and obtain three counting rules, ``AND'', ``OR'' and ``STACK'' rules, depending on the softness of branes and the character of fields on the branes four dimensions. The choice determines the number of Kaluza-Klein towers contributing to renormalization group equations, leading to a remarkable change in the running behavior of coupling constants.

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arXiv2001

Fermion Mass Hierarchies and Small Mixing Angles from Extra Dimensions

In this paper we study renormalization-group evolutions of Yukawa matrices enhanced by Kaluza-Klein excited modes and analyze their infrared fixed-point structure. We derive necessary conditions to obtain hierarchies between generations on the fixed point. These conditions restrict how the fields in the models can extend to higher dimension. Several specific mechanisms to realize the conditions are presented. We also take account of generation mixing effects and find a scenario where the mixing angles become small at low energy even with large initial values at high-energy scale. A toy model is shown to lead realistic quark mass matrices.

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arXiv2000

Twisted Family Structure and Neutrino Large Mixing

I demonstrate that neutrino large mixing between $ν_μ$ and $ν_τ$ are naturally reproduced using a novel mechanism called `E-twisting'in a supersymmetric $E_6$ grand unification model. This model explains all the characteristic features of the quark/lepton Dirac masses as well as the neutrino's Majorana masses despite the fact that all the members in {\bf27} of each generation are assigned a common family charge. Most remarkably, this model yields a novel relation which gives the 2-3 lepton mixing angle $θ_{μτ}$ in terms of quark masses and CKM mixing: $\tanθ_{μτ}=(m_b/m_s)V_{cb}$, which is a kind of SO(10) GUT relation similar to the celebrated SU(5) bottom-tau mass ratio. This relation is a result of a common `twisted SO(10)' structure.+

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arXiv2000

Novel Relations between Lepton and Quark Mixings

A novel relation is found which gives the 2-3 lepton mixing angle in terms of quark masses and CKM mixing: \tanθ_{μτ}=(m_b/m_s)V_{cb}. This relation, which is remarkably in good agreement with the quark data and the large lepton mixing recently observed, is a kind of SO(10) GUT relation similar to the celebrated bottom-tau mass ratio in SU(5). The GUT models in which this relation hold should have a `twisted SO(10)' structure between the second and third generations, in order to really explain the large lepton mixing, or equivalently, the right-hand side of the relation.

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arXiv2000

Yukawa hierarchy from extra dimensions and infrared fixed points

We discuss the existence of hierarchy of Yukawa couplings in the models with extra spatial dimensions. The hierarchical structure is induced by the power behavior of the cutoff dependence of the evolution equations which yield large suppressions of couplings at the compactification scale. The values of coupling constants at this scale can be made stable almost independently of the initial input parameters by utilizing the infrared fixed point. We find that the Yukawa couplings converge to the fixed points very quickly because of the enhanced energy dependence of the suppression factor from extra dimensions as well as in the case of large gauge couplings at high-energy scale.

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arXiv1999

Neutrino Masses in E_6 Unification

We show that the neutrino masses with large mixing between ν_μand ν_τare naturally reproduced in a supersymmetric E_6 grand unification model with an anomalous U(1)_X symmetry. We propose a simple scenario which incorporates a novel mechanism called `E-twisting' by which all the characteristic features of the fermion mass matrices, not only the quark/lepton's Dirac masses but also the neutrino's Majorana masses, can be well reproduced despite all the members in 27 of each generation are assigned a common U(1)_X charge.

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arXiv1998

Right-handed neutrino mass and bottom-tau ratio in strong coupling unification

The recent results of neutrino experiments indicate the existence of the right-handed neutrinos with masses around intermediate scale, which affects the prediction of the bottom-tau mass ratio. In the minimal supersymmetric standard model, this effect largely depends on the right-handed neutrino mass scale and then may severely limit its lower bound. In this letter, we show that in the case of strong coupling unification the bottom-tau mass ratio is little affected by the presence of the right-handed neutrinos. This is because of the infrared fixed-point behavior of Yukawa couplings, which is a common feature of this kind of model.

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arXiv1998

Sterile Neutrinos in a Grand Unified Model

The recent experimental results indicating the neutrino oscillations may strongly suggest that at least one more light neutrino species is required in order to reconcile the existing data. In the simple GUT frameworks, this fact seems difficult to preserve the parallelism between quarks and leptons. In this letter, we investigate an SO(10) grand unified model with a pair of extra generations in addition to the known three ones. Using the GUT relations, the obtained neutrino mass matrix naturally indicates that one of the SU(2) singlet (sterile) neutrino is very light and has large mixing with muon neutrino, which can explain the atmospheric neutrino anomaly, and the hot dark matter neutrino is also provided. The solar neutrino problem can be solved by the mixing with muon neutrino consistently with quark mixing, namely, the Cabibbo angle.

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arXiv1998

Analysis of Optimal Velocity Model with Explicit Delay

We analyze Optimal Velocity Model (OVM) with explicit delay. The properties of congestion and the delay time of car motion are investigated by analytical and numerical methods. It is shown that the small explicit delay time has almost no effects. In the case of the large explicit delay time, a new phase of congestion pattern of OVM seems to appear.

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arXiv1997

Infra-Red Fixed Points in an Asymptotically Non-Free Theory

We investigate the infrared fixed point structure in asymptotically free and asymptotically non-free theory. We find that the ratios of couplings converge strongly to their infrared fixed points in the asymptotically non-free theory.

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arXiv1997

Dynamical Gauge Bosons and Grand Unified Theory

We propose that the difference of dynamical gauge bosons in asymptotically non-free (ANF) gauge thoeries from elementary ones is the existence of the compositeness condition at some scale $Lambda$. This shall be explained by using non-linear Grassmannian like model where dynamical gauge bosons are generated associated with the hidden local symmetry. Then we argue that ANF gauge theories may provide another possible scenario of the ``standard model'' below GUT scale, where we shall see that infra-red stable points play essential roles. The talk is based on the papers written with J. Sato and K. Yoshioka, T. Takeuchi, T. Onogi and Y. Taniguchi and S. Tanimura (Invited talk at SCGT workshop held in Nagoya in Novenber 1996).

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arXiv1997

Predictions of $m_b/m_τ$ and $m_t$ in an Asymptotically Non-Free Theory

We discuss an extention of the Minimal Supersymmetric Standard Model (MSSM) with the 4th and anti-4th generations which have $SU(2)_L\times U(1)_Y$ invariant masses. Due to the the extra generations, all three running gauge couplings become asymptotically non--free while preserving gauge coupling unification at the GUT scale. We show that due to the asymptotically non--free character of the gauge couplings: (1) the top and bottom Yukawa couplings are strongly focused onto infrared fixed points as they are evolved down in scale making their values at $μ=\mz$ insensitive to their initial values at $μ=\mgut$; (2) the model predicts $\R(\mz) \equiv Y_b/Y_τ|_{μ=\mz}\approx 1.8$, which is consistent with the experimental value provided we take the ratio of Yukawa couplings at the GUT scale to be $\R(\mgut) = Y_b/Y_τ|_{μ= \mgut} = 1/3$; (3) the $t$ mass prediction comes out to be $\mt\approx 180\,\GeV$ which is also consistent with experiment.

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arXiv1996

Delay of Vehicle Motion in Traffic Dynamics

We demonstrate that in Optimal Velocity Model (OVM) delay times of vehicles coming from the dynamical equation of motion of OVM almost explain the order of delay times observed in actual traffic flows without introducing explicit delay times. Delay times in various cases are estimated: the case of a leader vehicle and its follower, a queue of vehicles controlled by traffic lights and many-vehicle case of highway traffic flow. The remarkable result is that in most of the situation for which we can make a reasonable definition of a delay time, the obtained delay time is of order 1 second.

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arXiv1994

Possible Candidates for SUSY SO(10) Model with an Intermediate Scale

We study the possibility of an intermediate scale existing in supersymmetric SO(10) grand unified theories: The intermediate scale is demanded to be around 10^{12} GeV so that neutrinos can obtain masses suitable for explaining the experimental data on the deficit of solar neutrino with Mikheev-Smirnov-Wolfenstein solution and the existence of hot dark matter. We show that any Pati-Salam type intermediate symmetries are excluded by requiring reasonable conditions and only $SU(2)_L\times SU(2)_R \times SU(3)_C\times U(1)_{B-L}$ is likely to be realized as an intermediate symmetry.

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arXiv1994

Hierarchical Mass Matrices in a Minimal SO(10) Grand Unification II

We continue to investigate the minimal SO(10)xU(1)_H model which we proposed recently. Renormalization group analysis of the model results in natural predictions of quark-lepton masses and Kobayashi-Maskawa matrix along with neutrino mixings adequate for solar neutrino oscillation.

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