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Yasuhiro Okada

Publications and source records attributed to Yasuhiro Okada.

At least 37 records · Page 2Linked to original sources
arXiv2008

Patterns of flavor signals in supersymmetric models

Quark and lepton flavor signals are studied in four supersymmetric models, namely the minimal supergravity model, the minimal supersymmetric standard model with right-handed neutrinos, SU(5) supersymmetric grand unified theory with right-handed neutrinos and the minimal supersymmetric standard model with U(2) flavor symmetry. We calculate b --> s(d) transition observables in B_d and B_s decays, taking the constraint from the B_s--B_s-bar mixing recently observed at Tevatron into account. We also calculate lepton flavor violating processes mu --> e gamma, tau --> mu gamma and tau --> e gamma for the models with right-handed neutrinos. We investigate possibilities to distinguish the flavor structure of the supersymmetry breaking sector with use of patterns of various flavor signals which are expected to be measured in experiments such as MEG, LHCb and a future Super B Factory.

hep-ph↗
arXiv2007

ILC Reference Design Report Volume 1 - Executive Summary

The International Linear Collider (ILC) is a 200-500 GeV center-of-mass high-luminosity linear electron-positron collider, based on 1.3 GHz superconducting radio-frequency (SCRF) accelerating cavities. The ILC has a total footprint of about 31 km and is designed for a peak luminosity of 2x10^34 cm^-2s^-1. This report is the Executive Summary (Volume I) of the four volume Reference Design Report. It gives an overview of the physics at the ILC, the accelerator design and value estimate, the detector concepts, and the next steps towards project realization.

physics.acc-ph↗
arXiv2007

Higgs Particle: The Origin of Mass

The Higgs particle is a new elementary particle predicted in the Standard Model of the elementary particle physics. It plays a special role in the theory of mass generation of quarks, leptons, and gauge bosons. In this article, theoretical issues on the Higgs mechanism are first discussed, and then experimental prospects on the Higgs particle study at the future collider experiments, LHC and ILC, are reviewed. The Higgs coupling determination is an essential step to establish the mass generation mechanism, which could lead to a deeper understanding of particle physics.

hep-ph↗
arXiv2007

Lepton Flavour Violating tau Decays in the Left-Right Symmetric Model

The Left-Right symmetric extension of the Standard Model with Higgs isospin triplets can provide neutrino masses via a TeV scale seesaw mechanism. The doubly charged Higgs bosons H^{\pm\pm}_L and H^{\pm\pm}_R induce lepton flavour violating decays τ^\pm \to lll at tree-level via a coupling which is related to the Maki-Nakagawa-Sakata matrix (V_{\rm MNS}). We study the magnitude and correlation of τ^\pm \to lll and μ\to eγwith specific assumptions for the origin of the large mixing in V_{\rm MNS} while respecting the stringent bound for μ\to eee. It is also shown that an angular asymmetry for τ^\pm \to lll is sensitive to the relative strength of the H^{\pm\pm}_L and H^{\pm\pm}_R mediated contributions and provides a means of distinguishing models with doubly charged Higgs bosons.

hep-ph↗
arXiv2006

Cosmic Positron Signature from Dark Matter in the Littlest Higgs Model with T-parity

We calculate the flux of cosmic positrons from the dark matter annihilation in the littlest Higgs model with T-parity. The dark matter annihilates mainly into weak gauge bosons in the halo, and high energy positrons are produced through leptonic and hadronic decays of the bosons. We investigate a possibility to detect the positron signal in upcoming experiments such as PAMELA and AMS-02. We found that the dark matter signal can be distinguished from the background in the PAMELA experiment when the dark matter mass is less than 120 GeV and the signal flux is enhanced due to a small scale clustering of dark matter. Furthermore, the signal from the dark matter annihilation can be detected in the AMS-02 experiment, even if such enhancement does not exist. We also discuss the invisible width of the Higgs boson in this model.

hep-ph↗
arXiv2005

Electroweak baryogenesis and the triple Higgs boson coupling

We study collider signatures of electroweak baryogenesis in the two Higgs doublet model and the minimal supersymmetric standard model. It is found that the trilinear coupling of the lightest Higgs boson receives large quantum corrections if the electroweak phase transition is strongly first order for successful baryogenesis. In the two Higgs doublet model, the magnitude of the deviation from the standard model value is shown to be larger than 10 percent. Such a deviation can be detected at a future electron-positron linear collider.

hep-ph↗
arXiv2005

Tauonic B decays in the Minimal Supersymmetric Standard Model

We study new physics effects on B decay processes including a final $τ$ particle, namely $B \to D τν$ and $B \to τν$. An important feature of these processes is that a charged Higgs boson can contribute to the decay amplitude at the tree level in models such as Two Higgs Doublet Model and the Minimal Supersymmetric Standard Model (MSSM). We derive a resummed effective Lagrangian for charged-Higgs mediated interactions in the MSSM with the Minimal Flavor Violation. Including supersymmetric (SUSY) loop corrections for down-type-quark and charged-lepton Yukawa couplings, we calculate the branching ratios of the $B \to D τν$ and $B \to τν$ processes. We find that SUSY correction due to gluino-sbottom diagrams can change the Higgs exchange contribution by $\pm50$%, whereas stau-neutralino diagrams can make corrections up to 20%. We also discuss relationship between SUSY corrections in the tauonic decays and flavor changing neutral current processes such as $B_s \to μ^+μ^-$ and $b \to s γ$.

hep-ph↗
arXiv2004

Electroweak baryogenesis and quantum corrections to the triple Higgs boson coupling

A phenomenological consequence of electroweak baryogenesis is studied in connection with the Higgs physics. In a two Higgs double model, the first order phase transition can be strong enough to allow the electroweak baryogenesis due to the effect of extra Higgs bosons. We investigate the quantum correction to the triple coupling of the lightest Higgs boson in such a scenario, and find that the condition of the strong first order phase transition necessarily leads to the deviation of at least 10 percent from the standard model prediction. Such magnitude of the deviation can be identified in future $e^+e^-$ linear collider experiments. We also discuss the minimal supersymmetric standard model with the light stop scenario, and point out that a sizable correction appears in the triple coupling for successful electroweak baryogenesis.

hep-ph↗
arXiv2004

The Linear Collider Physics Case: International Response to the Technology Independent Questions Posed by the International Technology Recommendation Panel

The International Technology Recommendation Panel distributed a list of questions to each major laboratory. Question 30, part b and d, were technology independent and related to the physics goals of the Linear Collider. An international panel, with representation from Asia, Europe, and the Americas, was formed by the World Wide Study during LCWS04 to formulate a response. This is given below and constitutes the response of the world-wide Linear Collider community.

hep-ph↗
arXiv2004

New physics from Higgs self-coupling measurement

Radiative correction to the triple Higgs boson coupling is studied in the two Higgs doublet model in connection with the electroweak baryogenesis. It is shown that the one loop correction is large enough to be identified in future linear collider experiments, if the baryon number of the Universe is generated at the first order electroweak phase transition.

hep-ph↗
arXiv2004

Higgs coupling constants as a probe of new physics

We study new physics effects on the couplings of weak gauge bosons with the lightest CP-even Higgs boson ($h$), $hZZ$, and the tri-linear coupling of the lightest Higgs boson, $hhh$, at the one loop order, as predicted by the two Higgs doublet model. Those renormalized coupling constants can deviate from the Standard Model (SM) predictions due to two distinct origins; the tree level mixing effect of Higgs bosons and the quantum effect of additional particles in loop diagrams. The latter can be enhanced in the renormalized $hhh$ coupling constant when the additional particles show the non-decoupling property. Therefore, even in the case where the $hZZ$ coupling is close to the SM value, deviation in the $hhh$ coupling from the SM value can become as large as plus 100 percent, while that in the $hZZ$ coupling is at most minus 1 percent level. Such large quantum effect on the Higgs tri-linear coupling is distinguishable from the tree level mixing effect, and is expected to be detectable at a future linear collider.

hep-ph↗
arXiv2004

Searching for New Physics through LFV Processes

Muon lepton flavor processes are reviewed in connection with search for physics beyond the standard model. Several methods to distinguish different theoretical models are discussed for $μ\to e γ$, $μ\to 3 e$, and $μ- e$ conversion processes. New calculation of the $μ- e$ conversion rate is presented including a Higgs boson mediated effect in the supersymmetric seesaw model.

hep-ph↗
arXiv2003

Exploring flavor structure of supersymmetry breaking from rare B decays and unitarity triangle

We study effects of supersymmetric particles in various rare B decay processes as well as in the unitarity triangle analysis. We consider three different supersymmetric models, the minimal supergravity, SU(5) SUSY GUT with right-handed neutrinos, and the minimal supersymmetric standard model with U(2) flavor symmetry. In the SU(5) SUSY GUT with right-handed neutrinos, we consider two cases of the mass matrix of the right-handed neutrinos. We calculate direct and mixing-induced CP asymmetries in the b to s gamma decay and CP asymmetry in B_d to phi K_S as well as the B_s--anti-B_s mixing amplitude for the unitarity triangle analysis in these models. We show that large deviations are possible for the SU(5) SUSY GUT and the U(2) model. The pattern and correlations of deviations from the standard model will be useful to discriminate the different SUSY models in future B experiments.

hep-ph↗
arXiv2003

Higgs-mediated muon-electron conversion process in supersymmetric seesaw model

We study the effect of the Higgs-exchange diagram for the lepton flavor violating muon-electron conversion process in nuclei in the supersymmetric seesaw model. The contribution is significant for a large value of tan beta and a small value of a neutral heavy Higgs boson mass, in which case the ratio of the branching ratios of B(mu N -> e N) / B(mu -> e gamma) is enhanced. We also show that the target atom dependence of the conversion branching ratio provides information on the size of the Higgs exchange diagram.

hep-ph↗
arXiv2003

New Physics Effect on the Higgs Self-Coupling

One-loop corrections to the self-coupling constant of the lightest CP-even Higgs boson are studied in the two Higgs doublet model. After renormalization is performed, quartic contributions of heavy particle's mass can appear in the effective coupling. We find that these non-decoupling effects can yield ${\cal O}(100)$ % deviations from the Standard Model prediction, even when all the other couplings of the lightest Higgs boson to gauge bosons and fermions are in good agreement with the Standard Model.

hep-ph↗