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Yasuhiro Okada

Publications and source records attributed to Yasuhiro Okada.

At least 55 records · Page 3Linked to original sources
arXiv2002

Exploring Flavor Structure of Supersymmetry Breaking at B factories

We investigate flavor physics at present and future B factories in order to distinguish supersymmetric models. We evaluate CP asymmetries in various B decay modes, Delta M(Bd), Delta M(Bs), and epsilon_K in three supersymmetric models, i.e. the minimal supergravity, the SU(5) SUSY GUT with right handed neutrinos, and a supersymmetric model with U(2) flavor symmetry. The allowed regions of Delta M(Bs)/Delta M(Bd) and CP asymmetries in B to J/psi K_S and b to s gamma are different for the three models so that it is possible to distinguish the three models by precise determinations of these observables in near future experiments.

hep-ph↗
arXiv2002

New Physics Search via the Higgs Self-Coupling

We discuss quantum corrections of new physics to the triple coupling of the lightest CP-even Higgs boson in the Two Higgs Doublet Model (THDM) and also in the Minimal Supersymmetric Standard Model (MSSM). In the THDM, quartic contributions of the mass of heavy particles in the loop can appear, which are not absorbed by renormalization of the Higgs boson mass. Such non-decoupling effects on the self-coupling can give corrections of ${\cal O}(100%)$, even when all measured Higgs couplings with gauge bosons and fermions are consistent with the Standard Model prediction. In the MSSM, the loop-corrections decouple in such a scenario.

hep-ph↗
arXiv2002

Detailed calculation of lepton flavor violating muon-electron conversion rate for various nuclei

The coherent muon-electron conversion rates in various nuclei are calculated for general lepton flavor violating interactions. We solve the Dirac equations numerically for the initial state muon and the final state electron in the Coulomb force, and perform the overlap integrals between the wave functions and the nucleon densities. The results indicate that the conversion branching ratio increases for a light nucleus up to the atomic number Z ~ 30, is largest for Z = 30 -- 60, and becomes smaller for a heavy nucleus with Z > (~ 60). We also discuss the uncertainty from the input proton and neutron densities. The atomic number dependence of the conversion ratio calculated here is useful to distinguish theoretical models with lepton flavor violation.

hep-ph↗
arXiv2002

Exploring Flavor Structure of Supersymmetry Breaking at B factories

We investigate quark flavor signals in three different supersymmetric models, the minimal supergravity, the SU(5) SUSY GUT with right handed neutrinos, and the minimal supersymmetric standard model with U(2) flavor symmetry, in order to study physics potential of the present and future $B$ factories. We evaluate CP asymmetries in various B decay modes, $Δm_{B_s}$, $Δm_{B_d}$, and $ε_K$. The allowed regions of the CP asymmetry in $B\to J/ψK_S$ and $Δm_{B_s}/Δm_{B_d}$ are different for the three models so that precise determinations of these observables in near future experiments are useful to distinguish the three models. We also investigate possible deviations from the standard model predictions of CP asymmetries in other B decay modes. In particular, a large deviation is possible for the U(2) model. The consistency check of the unitarity triangle including $B\to ππ,ρπ,D^{(*)}K^{(*)},D^{(*)}π,D^{*}ρ$, and so on, at future high luminosity $e^+e^-$ $B$ factories and hadronic $B$ experiments is therefore important to distinguish flavor structures of different supersymmetric models.

hep-ph↗
arXiv2001

Lepton flavor violating process in a supersymmetric grand unified theory with right-handed neutrino

Motivated from the recent results of neutrino oscillation experiment, we investigated lepton flavor violating (LFV) processes in a SU(5) supersymmetric grand unified theory with right-handed neutrino. The current experimental upper bound for $μ\to eγ$ process gives already some constraint on the model. Correlation between $μ\to e γ$ and the SUSY contribution to the muon anomalous magnetic moment is also discussed. Future LFV experiments will give considerable impacts on this type of SUSY GUT models equipped with seesaw neutrino mass generation.

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arXiv2001

Phenomenology of Higgs bosons in the Zee-Model

To generate small neutrino masses radiatively, the Zee-model introduces two Higgs doublets and one weak-singlet charged Higgs boson to its Higgs sector. From analyzing the renormalization group equations, we determine the possibile range of the lightest CP-even Higgs boson ($h$) mass and the Higgs boson self-couplings as a function of the cut-off scale beyond which either some of the coupling constants are strong enough to invalidate the perturbative analysis or the stability of the electroweak vacuum is no longer guaranteed. Using the results obtained from the above analysis, we find that the singlet charged Higgs boson can significantly modify the partial decay width of $h \to γγ$ via radiative corrections, and its collider phenomenology can also be drastically different from that of the charged Higgs bosons in the usual two-Higgs-doublet models.

hep-ph↗
arXiv2001

Muon anomalous magnetic moment, lepton flavor violation, and flavor changing neutral current processes in SUSY GUT with right-handed neutrino

Motivated by the large mixing angle solutions for the atmospheric and solar neutrino anomalies, flavor changing neutral current processes and lepton flavor violating processes as well as the muon anomalous magnetic moment are analyzed in the framework of SU(5) SUSY GUT with right-handed neutrino. In order to explain realistic mass relations for quarks and leptons, we take into account effects of higher dimensional operators above the GUT scale. It is shown that the supersymmetric (SUSY) contributions to the CP violation parameter in $K^0-\bar{K}^0$ mixing, $ε_K$, the $μ\to e γ$ branching ratio, and the muon anomalous magnetic moment become large in a wide range of parameter space. We also investigate correlations among these quantities. Within the current experimental bound of $\text{B}(μ\to e γ)$, large SUSY contributions are possible either in the muon anomalous magnetic moment or in $ε_K$. In the former case, the favorable value of the recent muon anomalous magnetic moment measurement at the BNL E821 experiment can be accommodated. In the latter case, the allowed region of the Kobayashi-Maskawa phase can be different from the prediction within the Standard Model (SM) and therefore the measurements of the CP asymmetry of $B\to J/ψK_S$ mode and $Δm_{B_s}$ could discriminate this case from the SM. We also show that the $τ\to μγ$ branching ratio can be close to the current experimental upperbound and the mixing induced CP asymmetry of the radiative B decay can be enhanced in the case where the neutrino parameters correspond to the Mikheyev-Smirnov-Wolfenstein small mixing angle solution.

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arXiv2001

Extracting SUSY Parameters from the Higgs Boson Properties

We calculate the ratio of the two branching ratios, Br(h -> bb-bar) and Br(h -> cc-bar) + Br(h -> gg), in the minimal supersymmetric standard model taking into account the SUSY-loop corrections to the Higgs sector and the hbb-bar vertex. We show that the heavy Higgs mass can be extracted from the ratio, almost independently of other SUSY parameters, in the region of tan(beta) ~< 10.

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arXiv2000

P and T Odd Asymmetries in Lepton Flavor Violating Tau Decays

We calculated the differential cross sections of the processes in which one of the pair created tau particles at an e^+ e^- collider decays into lepton flavor violating final states e.g. tau -> mu gamma, tau -> 3 mu, tau -> mu ee. Using the correlations between angular distributions of both sides of tau decays, we can obtain information on parity and CP violations of lepton flavor non-conserving interactions. The formulae derived here are useful in distinguishing different models, since each model of physics beyond the standard model predicts different angular correlations. We also calculate angular distributions of the major background process to tau -> l gamma search, namely tau -> l nu \barν gamma, and discuss usefulness of the angular correlation for background suppression.

hep-ph↗
arXiv2000

Another Look at Charged Higgs Boson Production at LEP

The current atmospheric and solar neutrino experimental data favors the bi-maximal mixing solution of the Zee-type neutrino mass matrix in which neutrino masses are generated radiatively. This model requires the existence of a weak singlet charged Higgs boson. While low energy data are unlikely to further constrain the parameters of this model, the direct search of charged Higgs production at the CERN LEP experiments can provide useful information on this mechanism of neutrino mass generation by analyzing their data with electrons and/or muons (in contrast to taus or charms) in the final state with missing transverse energies. We also discuss the difference in the production rates of a weak singlet from a weak doublet charged Higgs boson pairs at LEP.

hep-ph↗
arXiv2000

Neutrino Yukawa couplings and FCNC processes in B decays in SUSY-GUT

Flavor changing neutral current and lepton flavor violating processes are studied in the SU(5) SUSY-GUT with right-handed neutrino supermultiplets. Using input parameters motivated by neutrino oscillation, it is shown that the time-dependent CP asymmetry of $b \to s γ$ can be as large as 20%. We also show that the $B_s$-$\bar{B}_s$ mixing can be significantly different from the standard model prediction.

hep-ph↗
arXiv2000

Manifestaion of SUSY in B decays

SUSY effects on various flavor changing neutral current processes are discussed in the minimal supergravity model and the SU(5) grand unified theory with right-handed neutrino supermultiplets. In particular, in the latter case the neutrino Yukawa coupling constants can be a source of the flavor mixing in the right-handed-down-type-squark sector. It is shown that due to this mixing the time-dependent CP asymmetry of radiative B decay can be as large as 30% and the ratio of $B_s$-$\bar{B}_s$ mixing and $B_d$-$\bar{B}_d$ mixing deviates from the prediction in the standard model and the minimal supergravity model without the neutrino interaction.

hep-ph↗
arXiv2000

Neutrino oscillation, SUSY GUT and B decay

Effects of supersymmetric particles on flavor changing neutral current and lepton flavor violating processes are studied in the supersymmetric SU(5) grand unified theory with right-handed neutrino supermultiplets. Using input parameters motivated by neutrino oscillation, it is shown that the time-dependent CP asymmetry of radiative B decay can be as large as 30% when the $τ\to μγ$ branching ratio becomes close to the present experimental upper bound. We also show that the $B_s$--$\bar{B}_s$ mixing can be significantly different from the presently allowed range in the standard model.

hep-ph↗
arXiv1999

Mass bounds of the lightest CP-even Higgs boson in the two-Higgs-doublet model

The upper and the lower bounds of the lightest CP-even Higgs-boson mass ($m_h$) are discussed in the two-Higgs-doublet model (2HDM) with a softly-broken discrete symmetry. They are obtained as a function of a cut-off scale $Λ$ ($\leq 10^{19}$ GeV) by imposing the conditions in which the running coupling constants neither blow up nor fall down below $Λ$. In comparison with the standard model (SM), although the upper bound does not change very much, the lower bound is considerably reduced. In the decoupling regime where only one Higgs boson ($h$) becomes much lighter than the others, the lower bound is given, for example, by about 100 GeV for $Λ= 10^{19}$ GeV and $m_t = 175$ GeV, which is smaller by about 40 GeV than the corresponding lower bound in the SM. In generic cases, $m_h$ is no longer bounded from below by these conditions. If we consider the $b \to s γ$ constraint, small values of $m_h$ are excluded in Model II of the 2HDM.

hep-ph↗
arXiv1999

Indirect Search for Supersymmetry

Effects of supersymmetric particles may appear in various low energy experiments through loop diagrams. We discuss various flavor changing neutral current processes, the muon anomalous magnetic moment and lepton flavor violation in the context of the supergravity model. In particular the $B^0$-$\ol{B}^0$ mixing and the muon anomalous magnetic moment are revisited taking into account the recent Higgs boson search result. We also consider $μ^+ \to e^+ γ$ and $μ^+ \to e^+ e^+ e^-$ processes with polarized muons. We calculate the P-odd and T-odd asymmetries in these processes for SU(5) and SO(10) supersymmetric grand unified theories and show that these asymmetries are useful to distinguish different models.

hep-ph↗
arXiv1999

Muon Decay and Physics Beyond the Standard Model

This article reviews the current theoretical and experimental status of the field of muon decay and its potential to search for new physics beyond the Standard Model. The importance of rare muon processes with lepton flavor violation is highly stressed, together with precision measurements of normal muon decay. Recent up-to-date motivations of lepton flavor violation based on supersymmetric models, in particular supersymmetric grand unified theories, are described along with other theoretical models. Future prospects of experiments and muon sources of high intensity for further progress in this field are also discussed.

hep-ph↗
arXiv1999

Flavor changing neutral current processes and the muon anomalous magnetic moment in the supergravity model

Flavor changing neutral current processes in B and K decays in the supergravity model are revisited taking into account the recent progress of Higgs boson search experiments at LEP. Possible deviations of B^0--$\bar{B}^0$ mixing, the CP violating K^0--$\bar{K}^0$ mixing parameter $ε_K$ from the standard model predictions are reduced significantly in a small $\tanβ$ region due to the constraints on the SUSY parameter space imposed by the Higgs boson search. With the present bound on the Higgs boson mass, the magnitude of the B^0--$\bar{B}^0$ mixing amplitude can be enhanced up to 12% for $\tanb=3$ in the minimal supergravity. If we relax the strict universality of SUSY breaking scalar masses at the GUT scale, the deviation can be 25%. We also investigate SUSY contributions to the muon anomalous magnetic moment in the supergravity model and show that there is a correlation with the $b \to s γ$ amplitude. The SUSY contribution to $a_μ= \frac{(g-2)_μ}{2}$ can be (-30 -- $+80)\times 10^{-10}$ for $\tanβ=10$ and even larger for larger $\tanβ$. The improved measurement of the muon anomalous magnetic moment in the on-going experiment at BNL will put a strong constraint on SUSY parameter space, especially for a large $\tanβ$ region.

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