arXiv subjects

Takeshi Fukuyama

Publications and source records attributed to Takeshi Fukuyama.

108 records · Page 6Linked to original sources

arXiv2004

Lepton Flavour Violation in the Minimal SO(10) GUT Model and in the Standard Model with additional Heavy Dirac Neutrinos

Lepton flavour violation is considered in two models, Standard Model with additional heavy Dirac neutrinos and minimal supersymmetric standard model (MSSM) with SO(10) theoretical frame and minimal SUGRA (mSUGRA) SUSY-breaking mediation mechanism. The models are briefly explained. The structure of the amplitudes for neutrinoless decays of the lepton into a lepton and semileptonic neutrinoless decays of a lepton is given. The method for identification of meson content in the quark currents is exposed. The comparison of the amplitudes is made showing which of the processes have the largest branching ratios. The numerical results for the dominant decay rates are presented.

hep-ph↗

arXiv2004

Neutrino Magnetic Moments and Minimal Supersymmetric SO(10) Model

We examine supersymmetric contributions to transition magnetic moments of Majorana neutrinos. We first give the general formula for it. In concrete evaluations, informations of neutrino mass matrix elements including CP phases are necessary. Using unambiguously determined neutrino mass matrices in recently proposed minimal supersymmetric SO(10) model, the transition magnetic moments are calculated. The resultant neutrino magnetic moments are found to be roughly an order of magnitude larger than those calculated in the standard model extended to incorporate the see-saw mechanism.

hep-ph↗

arXiv2004

Detailed Analysis of Proton Decay Rate in the Minimal Supersymmetric SO(10) Model

We consider the minimal supersymmetric SO(10) model, where only one {\bf 10} and one $\bar{\bf 126}$ Higgs multiplets have Yukawa couplings with matter multiplets. This model has the high predictive power for the Yukawa coupling matrices consistent with the experimental data of the charged fermion mass matrices, and all the Yukawa coupling matrices are completely determined once a few parameters in the model are fixed. This feature is essential for definite predictions to the proton decay rate through the dimension five operators. We analyze the proton decay rate for the dominant decay modes $p \to K^{+} \barν$ by including as many free parameters as possible and varying them. There are two free parameters in the Yukawa sector, while five in the Higgsino sector. It is found that an allowed region exists when the free parameters in the Higgs sector are tuned so as to cancel the proton decay amplitude. The resultant proton lifetime is proportional to $1/\tan^2 β$ and the allowed region eventually disappears as $\tan β$ becomes large.

hep-ph↗

arXiv2004

Supernova prompt neutronization neutrinos and neutrino magnetic moments

It is shown that the combined action of spin-flavor conversions of supernova neutrinos due to the interactions of their Majorana-type transition magnetic moments with the supernova magnetic fields and flavor conversions due to the mass mixing can lead to the transformation of ν_e born in the neutronization process into their antiparticles \barν_e. Such an effect would have a clear experimental signature and its observation would be a smoking gun evidence for the neutrino transition magnetic moments. It would also signify the leptonic mixing parameter |U_{e3}| in excess of 10^{-2}.

hep-ph↗

arXiv2004

General Formulation for Proton Decay Rate in Minimal Supersymmetric SO(10) GUT

We make an explicit formulation for the proton decay rate in the minimal renormalizable supersymmetric (SUSY) SO(10) model. In this model, the Higgs fields consist of ${\bf 10}$ and ${\bf \bar{126}}$ SO(10) representations in the Yukawa interactions with matter and of ${\bf 10}$, ${\bf \bar{126}}$, ${\bf 126}$, and ${\bf 210}$ representations in the Higgs potential. We present all the mass matrices for the Higgs fields contained in this minimal SUSY SO(10) model. Finally, we discuss the threshold effects of these Higgs fields on the gauge coupling unification.

hep-ph↗

arXiv2003

Lepton Flavor Violating Processes and Muon g-2 in Minimal Supersymmetric SO(10) Model

In the recently proposed minimal supersymmetric SO(10) model, the neutrino Dirac Yukawa coupling matrix, together with all the other fermion mass matrices, is completely determined once free parameters in the model are appropriately fixed so as to accommodate the recent neutrino oscillation data. Using this unambiguous neutrino Dirac Yukawa couplings, we calculate the lepton flavor violating (LFV) processes and the muon g-2 assuming the minimal supergravity scenario. The resultant rates of the LFV processes are found to be large enough to well exceed the proposed future experimental bound, while the magnitude of the muon g-2 can be within the recent result by Brookhaven E821 experiment. Furthermore, we find that there exists a parameter region which can simultaneously realize the neutralino cold dark matter abundance consistent with the recent WMAP data.

hep-ph↗

arXiv2003

Neutrino oscillation data versus minimal supersymmetric SO(10) model

We reconsider the minimal supersymmetric SO(10) model, where only one {\bf 10} and one $\bar{\bf 126}$ Higgs multiplets have Yukawa couplings with matter multiplets. The model is generalized to include CP-violating phases, and examined how well its predictions can meet the current neutrino oscillation data. Using the electroweak scale data about six quark masses, three angles and one CP-phase in the Cabibbo-Kobayashi-Maskawa matrix and three charged-lepton masses and given $\tan β$ (the ratio of vacuum expectation values of a pair of Higgs doublets), we obtain the Pontecorvo-Maki-Nakagawa-Sakata matrix and the ratio, $Δm_\odot^2/Δm_\oplus^2 $, as functions of only one free parameter in the model. In our analysis, one-loop renormalization group equations for the gauge couplings, the Yukawa couplings and the effective dimension-five operator are used to connect the data between the electroweak scale and the grand unification scale. Fixing the free parameter appropriately, we find, for example, $\sin^2 2 θ_{12} \sim 0.72$, $\sin^2 2 θ_{23} \sim 0.90$, $\sin^2 2 θ_{13} \sim 0.16$ and $Δm_\odot^2/Δm_\oplus^2 \sim 0.19$ with $\tan β= 45$, which are in agreement with the current neutrino oscillation data.

hep-ph↗

arXiv2003

Universal Texture of Quark and Lepton Mass Matrices

Against the conventional picture that the mass matrix forms in the quark sectors will take somewhat different structures from those in the lepton sectors, a possibility that all the mass matrices of quarks and leptons have the same form as in the neutrinos is investigated. For the lepton sectors, the model leads to a nearly bimaximal mixing with the prediction |U_{e3}|^2=m_e/2m_μ=0.0024 and \tan^2θ_{sol} \simeq m_{ν1}/m_{ν2}, and so on. For the quark sectors, it can lead to reasonable values of the CKM mixing matrix and masses: |V_{us}|\simeq \sqrt{m_d/m_s}, |V_{ub}| \simeq |V_{cb}|\sqrt{m_u/m_c}, |V_{td}| \simeq |V_{cb}|\cdot |V_{us}|, and so on.

hep-ph↗

arXiv2002

Universal Texture of Quark and Lepton Mass Matrices and a Discrete Symmetry Z_3

Recent neutrino data have been favourable to a nearly bimaximal mixing, which suggests a simple form of the neutrino mass matrix. Stimulated by this matrix form, a possibility that all the mass matrices of quarks and leptons have the same form as in the neutrinos is investigated. The mass matrix form is constrained by a discrete symmetry Z_3 and a permutation symmetry S_2. The model, of course, leads to a nearly bimaximal mixing for the lepton sectors, while, for the quark sectors, it can lead to reasonable values of the CKM mixing matrix and masses.

hep-ph↗

arXiv2002

Renormalization Group Equation of Quark-Lepton Mass Matrices in the SO(10) Model with Two Higgs Scalars

The renormalization group equations (RGEs) of the mass matrices of quarks and leptons in a SO(10) model with two Higgs scalars in the Yukawa coupling are studied. This model is the minimal model of SUSY and non-SUSY SO(10) GUT which can reproduce all the experimental data. Non-SUSY SO(10) GUT model has the intermediate energy phase, Pati-Salam phase, and passes through the symmetry breaking pattern, $SO(10) \to SU(2)_L \times SU(2)_R \times SU(4)_C \to SU(2)_L \times U(1)_Y \times SU(3)_C$. Though minimal, it has, after the Pati-Salam phase, four Higgs doublets in Yukawa interactions. We consider the RGE's of the Yukawa coupling constants of quarks and charged leptons and of the coupling constants of the dimension five operators of neutrinos corresponding to the above symmetry breaking pattern. The scalar quartic interactions are also incorporated.

hep-ph↗

arXiv2002

Leptogenesis in models with multi-Higgs bosons

We study the leptogenesis scenario in models with multi-Higgs doublets. It is pointed out that the washing-out process through the effective dimension five interactions, which has not been taken into account seriously in the conventional scenario, can be effective, and the resultant baryon asymmetry can be exponentially suppressed. This fact implies new possible scenario where the observed baryon asymmetry is the remnant of the washed out lepton asymmetry which was originally much larger than the one in the conventional scenario. Our new scenario is applicable to some neutrino mass matrix models which predict too large CP-violating parameter and makes them viable through the washing-out process.

hep-ph↗

arXiv2001

Gauge Transformations and Weak Lax Equation

We consider several integrable systems from a standpoint of the SL(2,R) invariant gauge theory. In the Drinfeld-Sokorov gauge, we get a one parameter family of nonlinear equations from zero curvature conditions. For each value of the parameter the equation is described by weak Lax equations. It is transformed to a set of coupled equations which pass the Painlevé test and are integrable for any integer values of the parameter. Performing successive gauge transformations (the Miura transformations) on the system of equations we obtain a series of nonlinear equations.

nlin.SI↗

arXiv2000

Relativistic Effects on Neutrino Pair Annihilation above a Kerr Black Hole with the Accretion Disk

Using idealized models of the accretion disk we investigate the relativistic effects on the energy deposition rate via neutrino pair annihilation near the rotation axis of a Kerr black hole. Neutrinos are emitted from the accretion disk. The bending of neutrino trajectories and the redshift due to the disk rotation and gravitation are taken into consideration. The Kerr parameter, $a$, affects not only neutrinos' behavior but also the inner radius of the accretion disk. When the deposition energy is mainly contributed by the neutrinos coming from the central part, the redshift effect becomes dominant as $a$ becomes large and the energy deposition rate is reduced compared with that neglecting the relativistic effects. On the other hand, for small $a$ the bending effect gets dominant and makes energy increase by factor 2 compared with that neglecting the relativistic effects. For the disk with temperature gradient, the energy deposition rate for a small inner radius of the accretion disk is smaller than that estimated by neglecting the relativistic effects. The relativistic effects, especially for large $a$, play a negative role in avoiding the baryon contamination problem in gamma-ray bursts.

astro-ph↗

arXiv2000

Neutrino Pair Annihilation in the Gravitation of Gamma Ray Burst Sources

We study semianalytically the gravitational effects on neutrino pair annihilation near the neutrinosphere and around the thin accretion disk. For the disk case, we assume that the accretion disk is isothermal and that the gravitational field is dominated by the Schwarzschild black hole. General relativistic effects are studied only near the rotation axis. The energy deposition rate is enhanced by the effect of orbital bending toward the center. However, the effects of the redshift and gravitational trapping of the deposited energy reduce the effective energy of the gamma ray bursts' source. Although each effect is substantial, the effects partly cancel one another. As a result, the gravitational effects do not substantially change the energy deposition rate for either the spherical symmetric case or the disk case.

astro-ph↗

arXiv1998

Hierarchy of Higher Dimensional Integrable System

Integrable equations in ($1 + 1$) dimensions have their own higher order integrable equations, like the KdV, mKdV and NLS hierarchies etc. In this paper we consider whether integrable equations in ($2 + 1$) dimensions have also the analogous hierarchies to those in ($1 + 1$) dimensions. Explicitly is discussed the Bogoyavlenskii-Schiff(BS) equation. For the BS hierarchy, there appears an ambiguity in the Painlevé test. Nevertheless, it may be concluded that the BS hierarchy is integrable.

solv-int↗

arXiv1997

General Theorem about Gravitational Lensing

We study the general theorem about gravitational lensing which states the relationship between the numbers of images with different parities. Our formulation allows an extension to the nontransparent and singular model.

astro-ph↗

arXiv1996

Late-Time Mild Inflation --- a possible solution of dilemma: cosmic age and the Hubble parameter ---

We explore the cosmological model in which a late-time mild inflation is realized after the star formation epoch. Non-vanishing curvature coupling of a classical boson field yields this mild inflation without a cosmological constant. Accordingly the lifetime of the present Universe is remarkably increased in our model. Thus we show that the present observed high value of the Hubble parameter $H_0 \approx 70-80{\rm km/sec/Mpc}$ is compatible with the age of the oldest stars $14{\rm Gyr}$ without introducing the cosmological constant or the open Universe model. Moreover in our model, the local Hubble parameter becomes larger than the global one. Thus we show that the present observed local Hubble parameter measured by using the Cepheid variables is compatible with the global Hubble parameter measured by using the Sunyaev-Zeldovich effect. We also examine the energy conditions, evolution of the effective gravitational constant and the nucleosynthesis process.

astro-ph↗

arXiv1992

Mtric from Non-Metric Action of Gravity

The action of general relativity proposed by Capovilla, Jacobson and Dell is written in terms of $SO(3)$ gauge fields and gives Ashtekar's constraints for Einstein gravity. However, it does not depend on the space-time metric nor its signature explicitly. We discuss how the space-time metric is introduced from algebraic relations of the constraints and the Hamiltonian by focusing our attention on the signature factor. The system describes both Euclidian and Lorentzian metrics depending on reality assignments of the gauge connections. That is, Euclidian metrics arise from the real gauge fields. On the other hand, self-duality of the gauge fields, which is well known in the Ashtekar's formalism, is also derived in this theory from consistency condition of Lorentzian metric. We also show that the metric so determined is equivalent to that given by Urbantke, which is usually accepted as a definition of the metric for this system.

hep-th↗