arXiv subjects

Masahisa Matsuda

Publications and source records attributed to Masahisa Matsuda.

16 recordsLinked to original sources

arXiv2016

Quark CP-Phase and Froggatt-Nielsen Mechanism

On the basis of the Froggatt-Nielsen mechanism, we study quark flavor mixings in the $SU(6) \times SU(2)_R$ model. The characteristic structure of the CKM matrix is attributed to the hierarchical effective Yukawa couplings due to the Froggatt-Nielsen mechanism and also to the state-mixings beyond the MSSM. We elucidate the detailed form of the CKM matrix elements and find interesting relations between the \textit{CP} violating phase and three mixing angles. Taking the existing data of three mixing angles, we estimate the quark \textit{CP}-phase at $δ= (75 \pm 3)^{\circ}$. This result is in accord with observations.

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arXiv2003

Particle Spectra and Gauge Unification in $SU(6) \times SU(2)_R$ Model

We study the path from the string scale physics to the low-energy physics in the $SU(6) \times SU(2)_R$ string-inspired model with the flavor symmetry ${\bf Z}_M \times {\bf Z}_N \times \tilde{D}_4$. The flavor symmetry controls the mass spectra of heavy particles as well as those of quarks and leptons in the intermediate energy region ranging from the string scale ($\sim 10^{18} {\rm GeV}$) to the electroweak scale. In this paper we examine the mass spectra of heavy particles in detail in our model. The renormalization group evolution of the gauge couplings is studied up to two-loop order. A consistent solution of the gauge unification around the string scale is found by adjusting the spectra of the anti-generation matter fields.

hep-ph↗

arXiv2002

Precocious Gauge Symmetry Breaking in $SU(6) \times SU(2)_R$ Model

In the $SU(6) \times SU(2)_R$ string-inspired model, we evolve the couplings and the masses down from the string scale $M_S$ using the renormalization group equations and minimize the effective potential. This model has the flavor symmetry including the binary dihedral group $\tilde{D}_4$. We show that the scalar mass squared of the gauge non-singlet matter field possibly goes negative slightly below the string scale. As a consequence, the precocious radiative breaking of the gauge symmetry down to the standard model gauge group can occur. In the present model, the large Yukawa coupling which plays an important role in the symmetry breaking is identical with the colored Higgs coupling related to the longevity of the proton.

hep-ph↗

arXiv2000

Large lepton flavor mixings in $SU(6)\times SU(2)_R$ model

The lepton masses and mixings are studied on the basis of string inspired $SU(6)\times SU(2)_R$ model with global flavor symmetries. Provided that sizable mixings between lepton doublets $L$ and Higgsino-like fields $H_d$ with even R-parity occur and that seesaw mechanism is at work in the neutrino sector, the model can yield a large mixing angle solution with $\tan θ_{12}, \tan θ_{23} = Ø(\sqrtł)$ $(ł= 0.22)$, which is consistent with the recent experimental data on atmospheric and solar neutrinos. In the solution Dirac mass hierarchies in the neutrino sector cancel out with the heavy Majorana sector in large part due to seesaw mechanism. Hierarchical pattern of charged lepton masses can be also explained.

hep-ph↗

arXiv1998

Natural Neutrino Mass Matrix

Naturalness of the neutrino mass hierarchy and mixing is studied. First we select among 12 neutrino mixing patterns a few patterns, which could form the natural neutrino mass matrix. Further we show that if the Dirac neutrino mass matrix is taken as the natural one in the quark sector, then only two mixing patterns without the large mixing lead to the natural right-handed Majorana mass matrix. The rest of the chosen patterns with three degenerate mass solution lead to the unnatural right-handed Majorana mass matrix in the see-saw mechanism. Notice however, that for the chosen two natural patterns there could be a huge mass hierarchy such as ${\cal O}(10^{4\sim 6})$ in order to reproduce the inverse mass hierarchy of the light neutrinos.

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arXiv1997

New Possibility of Solving the Problem of Lifetime Ratio $τ(Λ_b) / τ(B_d)$

We discuss the problem of the large discrepancy between the observed lifetime ratio of $Λ_b$ to $B_d$ and the theoretical prediction obtained by the heavy quark effective theory. A new possibility of solving this problem is proposed from the viewpoint of operator product expansion and the lifetime ratio of $Ω_b$ to $B_d$ is predicted.

hep-ph↗

arXiv1996

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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arXiv1996

Semileptonic Decay of $B$-Meson into $D^{**}$ and the Bjorken Sum Rule

We study the semileptonic branching fraction of $B$-meson into higher resonance of charmed meson $D^{**}$ by using the Bjorken sum rule and the heavy quark effective theory(HQET). This sum rule and the current experiment of $B$-meson semileptonic decay into $D$ and $D^*$ predict that the branching ratio into $D^{**}lν_l$ is about 1.7\%. This predicted value is larger than the value obtained by the various theoretical hadron models based on the HQET.

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arXiv1995

Quark-Lepton Masses and the Ckm Matrix in a String Inspired Model

In the context of the Calabi-Yau string model we discuss the origin of characteristic pattern of quark-lepton masses and the CKM matrix. The discrete $R$-symmetry $Z_{2k+1} \times Z_2$ is introduced and the $Z_2$ is assigned to the $R$-parity. The gauge symmetry at the string scale is broken into the standard model gauge group at an intermediate energy scale. At energies below the intermediate scale down-type quarks and also leptons are mixed with unobserved heavy states, respectively. On the other hand, there are no such mixings for up-type quarks. The large mixings between light states and heavy ones cause different mass pattern of leptons and down-type quarks from that of up-type quarks and yield a nontrivial CKM matrix for quarks but a trivial one for leptons. The mixing mechanism is illustrated using a two-generation toy model.

hep-ph↗

arXiv1994

The Aligned $SU(5) \times U(1)^2$ Model

In Calabi-Yau string compactification, it is pointed out that there exists a new type of $SU(5) \times U(1)^2$ model (the aligned $SU(5) \times U(1)^2$ model) in which the $SU(5)$ differs from the standard $SU(5)$ and also from the flipped $SU(5)$. With the aid of the discrete symmetry suggested from Gepner model, we construct a simple and phenomenologically interesting three-generation model with the aligned $SU(5) \times U(1)^2$ gauge symmetry. The triplet-doublet splitting problem can be solved. It is also found that there is a realistic solution for solar neutrino problem and for the $μ$-problem. At low energies this model is in accord with the minimal supersymmetric standard model except for the existence of singlet fields with masses of $O(1)$TeV.

hep-ph↗

arXiv1994

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.

hep-ph↗

arXiv1994

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.

hep-ph↗

arXiv1994

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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arXiv1993

A Large Majorana-Mass From Calabi-Yau Superstring Models

In Calabi-Yau superstring models it is found that two large intermediate energy scales of symmetry breaking can be induced for special types of the nonrenormalizable interactions. In the models one set of $SO(10)$-singlet, right-handed neutrino and their mirror chiral superfields is needed. Through the study of the minimization of the scalarpotential, the conditions for the presence of two large intermediate scales are obtained. In this scheme a Majorana-mass possibly amounts to $O(10^{9 \sim 10}\gev)$. This large Majorana-mass solves the solar neutrino problem and also is compatible with the cosmological bound for stable light neutrinos.

hep-ph↗

arXiv1993

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.

hep-ph↗

arXiv1993

The String Unufication of Gauge Cuoplings and Gauge Kinetic Mixings

In the superstring models we have not only the complete {\bf 27} multiplets of $E_6$ but also extra incomplete $({\bf 27}+{\overline {\bf 27}})$ chiral supermultiplets being alive at low energies. Associated with these additional multiplets, when the gauge symmetry contains more than one $U(1)$ gauge group, there may exist gauge kinetic mixings among these $U(1)$ gauge groups. In such cases the effect of gauge kinetic mixings should be incorporated into the study of unification of gauge couplings. We study these interesting effects systematically in these models. The string threshold effect is also taken into account. It is found that in the four-generation models we do not have a advisable solution of string unification of gauge couplings consistent with experimental values at the electroweak scale. We also discuss the possible scenarios to solve this problem.

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