arXiv subjects

Nobuchika Okada

Publications and source records attributed to Nobuchika Okada.

At least 199 records · Page 11Linked to original sources

arXiv2011

Higgs inflation in minimal supersymmetric SU(5) GUT

The Standard Model Higgs boson with large nonminimal coupling to the gravitational curvature can drive cosmological inflation. We study this type of inflationary scenario in the context of supersymmetric grand unification and point out that it is naturally implemented in the {\em minimal} supersymmetric SU(5) model, and hence virtually in any GUT models. It is shown that with an appropriate Kähler potential the inflaton trajectory settles down to the Standard Model vacuum at the end of the slow roll. The predicted cosmological parameters are also consistent with the 7-year WMAP data.

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arXiv2011

Discrimination of New Physics Models with the International Linear Collider

The large hadron collider (LHC) is anticipated to provide signals of new physics at the TeV scale, which are likely to involve production of a WIMP dark matter candidate. The international linear collider (ILC) is to sort out these signals and lead us to some viable model of the new physics at the TeV scale. In this article, we discuss how the ILC can discriminate new physics models, taking the following three examples: the inert Higgs model, the supersymmetric model, and the littlest Higgs model with T-parity. These models predict dark matter particles with different spins, 0, 1/2, and 1, respectively, and hence comprise representative scenarios. Specifically, we focus on the pair production process, e+e- -> chi+chi- -> chi0chi0W+W-, where chi0 and chi+- are the WIMP dark matter and a new charged particle predicted in each of these models. We then evaluate how accurately the properties of these new particles can be determined at the ILC and demonstrate that the ILC is capable of identifying the spin of the new charged particle and discriminating these models.

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arXiv2011

Renormalization effects on the MSSM from a calculable model of a strongly coupled hidden sector

We investigate possible renormalization effects on the low-energy mass spectrum of the minimal supersymmetric standard model (MSSM), using a calculable model of strongly coupled hidden sector. We model the hidden sector by N=2 supersymmetric quantum chromodynamics with gauge group SU(2) x U(1) and N_f=2 matter hypermultiplets, perturbed by a Fayet-Iliopoulos term which breaks the supersymmetry down to N=0 on a metastable vacuum. In the hidden sector the Kahler potential is renormalized. Upon identifying a hidden sector modulus with the renormalization scale, and extrapolating to the strongly coupled regime using the Seiberg-Witten solution, the contribution from the hidden sector to the MSSM renormalization group flows is computed. For concreteness, we consider a model in which the renormalization effects are communicated to the MSSM sector via gauge mediation. In contrast to the perturbative toy examples of hidden sector renormalization studied in the literature, we find that our strongly coupled model exhibits rather intricate effects on the MSSM soft scalar mass spectrum, depending on how the hidden sector fields are coupled to the messenger fields. This model provides a concrete example in which the low-energy spectrum of MSSM particles that are expected to be accessible in collider experiments is obtained using strongly coupled hidden sector dynamics.

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arXiv2011

Gaugino Mediation Combined with the Bulk Matter Randall-Sundrum Model

We investigate a simple 5D extension of the Minimal Supersymmetric (SUSY) Standard Model (SM) that is combined with the bulk matter Randall-Sundrum (RS) model, which gives a natural explanation the Yukawa coupling hierarchy. In this model, matter and gauge superfields reside in the 5D bulk while a SUSY breaking sector and the Higgs doublet superfields are localized on the infrared brane. The Yukawa coupling hierarchy in SM can be naturally explained through the wavefunction localization of the matter superfields. While sparticles obtain their flavor-blind soft SUSY breaking masses dominantly from the gaugino-mediated SUSY breaking, flavor-violating soft terms arise through the gravity-mediated SUSY breaking which are controlled by the wavefunction localization of the matter superfields. This structure of the model allows us to predict the sparticle mass spectrum including flavor-violating terms. We first explicitly determine the 5D disposition of matter superfields from the low energy experimental data on SM fermion masses, CKM matrix and the neutrino oscillation parameters. Then, we calculate particle mass spectra and estimate the effects of the flavor-violating soft terms, which should be compared with the current experimental constraints. With gravitino being the lightest sparticle (LSP), the next-to-LSP, which is long-lived, is predicted most likely to be either singlet smuon-like or selectron-like. The model can be tested at collider experiments through flavor-violating processes involving sparticles. The flavor structure among sparticle, once observed, gives us a clue to deep understanding of the origin of Yukawa coupling hierarchy.

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arXiv2011

Non-Minimal B-L Inflation with Observable Gravity Waves

We consider non-minimal λϕ^4 inflation in a gauged non-supersymmetric U(1)_{B-L} model containing the gravitational coupling ξ\mathcal{R} Φ^\dagger Φ, where \mathcal{R} denotes the Ricci scalar and the standard model singlet inflaton field Φspontaneously breaks the U(1)_{B-L} symmetry. Including radiative corrections, the predictions 0.956 < n_s < 0.984 and 0.007 < r < 0.1 for the scalar spectral index and tensor to scalar ratio r lie within the current WMAP 1-σbounds. If the B-L symmetry breaking scale is of order a TeV or so, one of the three right handed neutrinos is a plausible cold dark matter candidate. Bounds on the dimensionless parameters λ, ξand the gauge coupling g_{B-L} are obtained.

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arXiv2011

Particle Spectroscopy of Supersymmetric SO(10) with Non-Universal Gaugino Masses

We examine the low scale particle spectroscopy of an SO(10) (or equivalently SU(5)) inspired supersymmetric model with non-universal gaugino masses. The model assumes minimal supergravity and contains the same number of fundamental parameters as the constrained minimal supersymmetric model (CMSSM.) Realistic solutions compatible with dark matter and other applicable experimental constraints are shown to exist for both positive and negative signs of the MSSM parameter mu. We present several benchmark points which will be tested at the LHC and by the ongoing direct and indirect dark matter detection experiments.

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arXiv2011

Resonant Leptogenesis in the Minimal B-L Extended Standard Model at TeV

We investigate the resonant leptogenesis scenario in the minimal B-L extended standard model(SM) with the B-L symmetry breaking at the TeV scale. Through detailed analysis of the Boltzmann equations, we show how much the resultant baryon asymmetry via leptogenesis is enhanced or suppressed, depending on the model parameters, in particular, the neutrino Dirac Yukawa couplings and the TeV-scale Majorana masses of heavy degenerate neutrinos. In order to consider a realistic case, we impose a simple ansatz for the model parameters and analyze the neutrino oscillation parameters and the baryon asymmetry via leptogenesis as a function of only a single CP-phase. We find that for a fixed CP-phase all neutrino oscillation data and the observed baryon asymmetry of the present universe can be simultaneously reproduced.

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arXiv2011

Recent MEG Results and Predictive SO(10) Models

Recent MEG results of a search for the lepton flavor violating (LFV) muon decay, $μ\to e γ$, show 3 events as the best value for the number of signals in the maximally likelihood fit. Although this result is still far from the evidence/discovery in statistical point of view, it might be a sign of a certain new physics beyond the Standard Model. As has been well-known, supersymmetric (SUSY) models can generate the $μ\to e γ$ decay rate within the search reach of the MEG experiment. A certain class of SUSY grand unified theory (GUT) models such as the minimal SUSY SO(10) model (we call this class of models "predictive SO(10) models") can unambiguously determine fermion Yukawa coupling matrices, in particular, the neutrino Dirac Yukawa matrix. Based on the universal boundary conditions for soft SUSY breaking parameters at the GUT scale, we calculate the rate of the $μ\to e γ$ process by using the completely determined Dirac Yukawa matrix in two examples of predictive SO(10) models. If we interpret the 3 events in MEG experiment as a positive signal and combine it with other experimental constraints such as the relic density of the neutralino dark matter and recent results on muon $g-2$, we can pin down a parameter set of the universal boundary conditions. Then, we propose benchmark sparticle mass spectra for each predictive SO(10) model, which will be tested at the Large Hadronic Collider.

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arXiv2011

Discrimination of Supersymmetric Grand Unified Models in Gaugino Mediation

We consider supersymmetric grand unified theory (GUT) with the gaugino mediated supersymmetry breaking and investigate a possibility to discriminate different GUT models in terms of predicted sparticle mass spectra. Taking two example GUT models, the minimal SU(5) and simple SO(10) models, and imposing a variety of theoretical and experimental constraints, we calculate sparticle masses. Fixing parameters of each model so as to result in the same mass of neutralino as the lightest supersymmetric particle (LSP), giving the observed dark matter relic density, we find sizable mass differences in the left-handed slepton and right-handed down-type squark sectors in two models, which can be a probe to discriminate the GUT models realized at the GUT scale far beyond the reach of collider experiments.

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arXiv2010

Higgs Boson Mass Bounds in Seesaw Extended Standard Model with Non-Minimal Gravitational Coupling

In the presence of non-minimal gravitational coupling $ ξH^\dagger H {\cal R}$ between the standard model (SM) Higgs doublet $H$ and the curvature scalar ${\cal R}$, the effective ultraviolet cutoff scale is given by $Λ_{\rm cut}\approx m_P/ξ$, where $m_P$ is the reduced Planck mass, and $ξ\gtrsim 1$ is a dimensionless coupling constant. In type I and type III seesaw extended SM, which can naturally explain the observed solar and atmospheric neutrino oscillations, we investigate the implications of this non-minimal gravitational coupling for the SM Higgs boson mass bounds based on vacuum stability and perturbativity arguments. A lower bound on the Higgs boson mass close to 120 GeV is realized with type III seesaw and $ξ\sim 10-10^3$.

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arXiv2010

WIMP Dark Matter Inflation with Observable Gravity Waves

We present a successful inflation model based on $λϕ^4$ potential in which a Standard Model (SM) singlet inflaton $ϕ$, with mass of around a TeV or less, also plays the role of a weakly interacting scalar dark matter particle (WIMP). The WIMP relic abundance generated after inflation is in accord with the current observations. The spectral index $n_s$ lies within the WMAP 1-$σ$ bounds, while the Planck satellite may observe the tensor-to-scalar ratio, a canonical measure of gravity waves, which we estimate lies between 0.003 and 0.007.An unbroken $Z_2$ parity ensures that the scalar WIMP is absolutely stable.

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arXiv2010

Location and Direction Dependent Effects in Collider Physics from Noncommutativity

We examine the leading order noncommutative corrections to the differential and total cross sections for e+ e- --> q q-bar. After averaging over the earth's rotation, the results depend on the latitude for the collider, as well as the direction of the incoming beam. They also depend on scale and direction of the noncommutativity. Using data from LEP, we exclude regions in the parameter space spanned by the noncommutative scale and angle relative to the earth's axis. We also investigate possible implications for phenomenology at the future International Linear Collider.

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arXiv2010

Observing the Coupling between Dark Matter and Higgs Boson at the ILC

One of the main purposes on physics at the International Linear Collider (ILC) is to study the property of dark matter such as its mass, spin, and interactions between the dark matter and particles in the standard model. Among those, the interaction between dark matter and higgs boson is important, because, if the dark matter is a weakly interacting massive particle, the existence of the dark matter is expected to relate to physics of electroweak symmetry breaking. In addition, the interaction plays an important role at direct detection experiments of dark matter. In this report, we discuss how accurately the coupling constant of the interaction can be measured at the ILC with the center of mass energy less than 500 GeV.

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arXiv2010

Measurement of Higgs Anomalous Coupling with H->WW* at International Linear Collider

The measurement of the Higgs coupling to W bosons is an important program at the international linear collider (ILC) to search for the anomaly in the coupling to the gauge bosons. We study the sensitivity of ILC to the Higgs anomalous coupling to W bosons by using ZH->vvWW* events. In this article, we report the status of the study.

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arXiv2010

Can WIMP Dark Matter overcome the Nightmare Scenario?

Even if new physics beyond the Standard Model (SM) indeed exists, the energy scale of new physics might be beyond the reach at the Large Hadron Collider (LHC) and the LHC could find only the Higgs boson but nothing else. This is the so-called "nightmare scenario". On the other hand, the existence of the dark matter has been established from various observations. One of the promising candidates for thermal relic dark matter is a stable and electric charge-neutral Weakly Interacting Massive Particle (WIMP) with the mass below the TeV scale. In the nightmare scenario, we introduce a WIMP dark matter singlet under the SM gauge group, which only couples to the Higgs doublet at the lowest order, and investigate a possibility that such WIMP dark matter can be a clue to overcome the nightmare scenario via various phenomenological tests such as the dark matter relic abundance, the direct detection experiments for the dark matter particle, and the production of the dark matter particle at the LHC.

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arXiv2010

Tensor to Scalar Ratio in Non-Minimal $ϕ^4$ Inflation

We reconsider non-minimal λϕ^4 chaotic inflation which includes the gravitational coupling term ξ\mathcal{R} ϕ^2, where ϕdenotes a gauge singlet inflaton field and \mathcal{R} is the Ricci scalar. For ξ>> 1 we require, following recent discussions, that the energy scale λ^{1/4} m_P / \sqrtξ for inflation should not exceed the effective UV cut-off scale m_P / ξ, where m_P denotes the reduced Planck scale. The predictions for the tensor to scalar ratio r and the scalar spectral index n_s are found to lie within the WMAP 1-σbounds for 10^{-12} < λ< 10^{-4} and 10^{-3} < ξ< 10^2. In contrast, the corresponding predictions of minimal λϕ^4 chaotic inflation lie outside the WMAP 2-σbounds. We also find that r > 0.002, provided the scalar spectral index n_s > 0.96. In estimating the lower bound on r we take into account possible modifications due to quantum corrections of the tree level inflationary potential.

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arXiv2010

Non-thermal Leptogenesis in a simple 5D SO(10) GUT

We discuss the non-thermal leptogenesis in the scheme of 5D orbifold SO(10) GUT with the smooth hybrid inflation. With an unambiguously determined Dirac Yukawa couplings and an assumption for the neutrino mixing matrix of the tri-bimaximal from, we analyze baryon asymmetry of the universe via non-thermal leptogenesis in two typical cases for the light neutrino mass spectrum, the normal and inverted hierarchical cases. The resultant baryon asymmetry is obtained as a function of the lightest mass eigenvalue of the light neutrinos, and we find that a suitable amount of baryon asymmetry of the universe can be produced in the normal hierarchical case, while in the inverted hierarchical case the baryon asymmetry is too small to be consistent with the observation.

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arXiv2010

Higgs portal dark matter in the minimal gauged $U(1)_{B-L}$ model

We propose a scenario of the right-handed neutrino dark matter in the context of the minimal gauged $U(1)_{B-L}$ model by introducing an additional parity which ensures the stability of dark matter particle. The annihilation of this right-handed neutrino takes place dominantly through the s-channel Higgs boson exchange, so that this model can be called Higgs portal dark matter model. We show that the thermal relic abundance of the right-handed neutrino dark matter with help of Higgs resonance can match the observed dark matter abundance. In addition we estimate the cross section with nucleon and show that the next generation direct dark matter search experiments can explore this model.

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