arXiv subjects

Nobuchika Okada

Publications and source records attributed to Nobuchika Okada.

At least 217 records · Page 12Linked to original sources

arXiv2009

Running Standard Model Inflation And Type I Seesaw

Several authors have recently argued that a satisfactory inflationary scenario can be implemented in the Standard Model (SM) by introducing a strong non-minimal coupling of the Higgs doublet to gravity. It is shown here that type I seesaw physics containing right handed neutrinos at intermediate scales can have a significant impact on the inflationary predictions of these models. For one such model, values of the scalar spectral index lower than the tree level prediction of 0.968 are realized for plausible values of the seesaw parameters and a SM Higgs boson mass close to 130 GeV. A precise measurement of n_s by PLANCK, as well as measurement of the Higgs boson mass by LHC should provide stringent tests of this SM based inflationary scenario supplemented by type I seesaw physics.

hep-ph↗

arXiv2009

Gauge-Higgs Dark Matter

When the anti-periodic boundary condition is imposed for a bulk field in extradimensional theories, independently of the background metric, the lightest component in the anti-periodic field becomes stable and hence a good candidate for the dark matter in the effective 4D theory due to the remaining accidental discrete symmetry. Noting that in the gauge-Higgs unification scenario, introduction of anti-periodic fermions is well-motivated by a phenomenological reason, we investigate dark matter physics in the scenario. As an example, we consider a five-dimensional SO(5)$\timesU(1)_X$ gauge-Higgs unification model compactified on the $S^1/Z_2$ with the warped metric. Due to the structure of the gauge-Higgs unification, interactions between the dark matter particle and the Standard Model particles are largely controlled by the gauge symmetry, and hence the model has a strong predictive power for the dark matter physics. Evaluating the dark matter relic abundance, we identify a parameter region consistent with the current observations. Furthermore, we calculate the elastic scattering cross section between the dark matter particle and nucleon and find that a part of the parameter region is already excluded by the current experimental results for the direct dark matter search and most of the region will be explored in future experiments.

hep-ph↗

arXiv2009

The PAMELA and Fermi signals from long-lived Kaluza-Klein dark matter

We propose a simple extension of the minimal universal extra dimension (UED)model by introducing a small curvature. The model is formulated as a small anti-de Sitter curvature limit of the five-dimensional standard model (SM) in the Randall-Sundrum background geometry. While the lightest Kaluza-Klein (KK) particle can be thermal relic dark matter as usual in the UED model, the KK-parity is explicitly broken in the presence of the small curvature and the KK dark matter decays into the SM fermions with a long lifetime. Couplings of the KK dark matter with SM fermion pairs in the five dimensional bulk are controlled by fermion bulk masses. With a suitable choice of bulk masses for leptons and quarks, the KK dark matter through its decay into leptons can account for the cosmic-ray electron/positron excesses reported by the recent PAMELA and FERMI satellite experiments, while suppressing the decay into quarks.

hep-ph↗

arXiv2009

The minimal B-L model naturally realized at TeV scale

In a previous paper, we have proposed the minimal B-L extended standard model as a phenomenologically viable model that realizes the Coleman-Weinberg-type breaking of the electroweak symmetry. Assuming the classical conformal invariance and stability up to the Planck scale, we will show in this paper that the model naturally predicts TeV scale B-L breaking as well as a light standard-model singlet Higgs boson and light right-handed neutrinos around the same energy scale. We also study phenomenology and detectability of the model at the Large Hadron Collider (LHC) and the International Linear Collider (ILC).

hep-ph↗

arXiv2009

Classically Conformal B-L extended Standard Model

Under a hypothesis of classically conformal theories, we investigate the minimal B-L extended Standard Model, which naturally provides the seesaw mechanism for explaining tiny neutrino masses. In this setup, the radiative gauge symmetry breaking is successfully realized in a very simple way: The B-L gauge symmetry is broken through the conformal anomaly induced by quantum corrections in the Coleman-Weinberg potential. Associated with this B-L symmetry breaking, the Higgs mass parameter is dynamically generated, by which the electroweak symmetry breaking is triggered. We find that a wide range of parameter space can satisfy both the theoretical and experimental requirements.

hep-ph↗

arXiv2009

Type II Seesaw and the PAMELA/ATIC Signals

We discuss how the cosmic ray signals reported by the PAMELA and ATIC/PPB-BETS experiments may be understood in a Standard Model (SM) framework supplemented by type II seesaw and a stable SM singlet scalar boson as dark matter. A particle physics explanation of the 'boost' factor can be provided by including an additional SM singlet scalar field.

hep-ph↗

arXiv2009

Influence of Z' boson on top quark spin correlations at the LHC

We study top-antitop pair production and top spin correlations in a model with an electrically neutral massive gauge boson, Z', at the Large Hadron Collider. In addition to the Standard Model processes, the Z' contributes to the top-antitop pair production process in the s-channel. Choosing a kinematical region of top invariant mass around the Z' resonance pole, we find sizable deviations of the top-antitop pair production cross section and the top spin correlations from those of the Standard Model.

hep-ph↗

arXiv2009

Effects of unparticle on top spin correlation at the Large Hadron Collider

We study effects of the scale invariant hidden sector, unparticle, proposed by Georgi, on top spin correlation at the Large Hadron Collider. Assuming no flavor changing interaction between the unparticles and the Standard Model particles, there arises the top-antitop quark pair production process through virtual unparticle exchanges in the s-channel in addition to the Standard Model processes. In particular, we consider contributions of scalar and vector unparticles and find that these make sizable deviations of the top spin correlation from the Standard Model one.

hep-ph↗

arXiv2009

Gauss-Bonnet braneworld cosmological effect on relic density of dark matter

In Gauss-Bonnet braneworld cosmology, the Friedmann equation of our four-dimensional universe on 3-brane is modified in a high energy regime (Gauss-Bonnet regime), while the standard expansion law is reproduced in low energies (standard regime). We investigate the Gauss-Bonnet braneworld cosmological effect on the thermal relic density of cold dark matter when the freeze-out of the dark matter occurs in the Gaugss-Bonnet regime. We find that the resultant relic density is considerably reduced when the transition temperature, which connects the Gauss-Bonnet regime with the standard regime, is low enough. This result is in sharp contrast with the result previously obtained in the Randall-Sundrum braneworld cosmology, where the relic density is enhanced.

hep-ph↗

arXiv2009

Tau-pair Performance in ILD detectors

Tau-pair process has been analyzed in the ILD detector model as a benchmark process for LoI. Results of background rejection, forward-backward asymmetry and polarization measurements are obtained with full detector simulation. Impact of detector parameters for tau-pair analysis is also discussed in this paper.

hep-ex↗

arXiv2008

Soft Probes of SU(5) Unification

We explore the sparticle and Higgs spectroscopy of an SU(5) inspired extension of the constrained minimal supersymmetric standard model (CMSSM). The universal soft parameter m_0 is replaced by m_{\bar 5} and m_{10}, where m_{\bar 5} and m_{10} denote universal soft scalar masses associated with fields in the five and ten dimensional representations of SU(5). The special case m_{\bar 5} << m_{10} yields a rather characteristic sparticle spectroscopy which can be tested at the LHC. We highlight a few benchmark points in which the lightest neutralino saturates the WMAP bound on cold dark matter abundance.

hep-ph↗

arXiv2008

Flavorful $Z^\prime$ signatures at LHC and ILC

There are lots of new physics models which predict an extra neutral gauge boson, referred as Z'-boson. In a certain class of these new physics models, the Z'-boson has flavor-dependent couplings with the fermions in the Standard Model (SM). Based on a simple model in which couplings of the SM fermions in the third generation with the Z'-boson are different from those of the corresponding fermions in the first two generations, we study the signatures of Z'-boson at the Large Hadron Collider (LHC) and the International Linear Collider (ILC). We show that at the LHC, the Z'-boson with mass around 1 TeV can be produced through the Drell-Yan processes and its dilepton decay modes provide us clean signatures not only for the resonant production of Z'-boson but also for flavor-dependences of the production cross sections. We also study fermion pair productions at the ILC involving the virtual Z'-boson exchange. Even though the center-of-energy of the ILC is much lower than a Z'-boson mass, the angular distributions and the forward-backward asymmetries of fermion pair productions show not only sizable deviations from the SM predictions but also significant flavor-dependences.

hep-ph↗

arXiv2008

NMSSM and Seesaw Physics at LHC

We consider extensions of the next-to-minimal supersymmetric model (NMSSM) in which the observed neutrino masses are described in terms of effective dimension six (or seven) rather than dimension five operators. All such operators respect the discrete symmetries of the model. The new particles associated with the double (or triple) seesaw mechanism can have sizable couplings to the known leptons, even with a TeV seesaw scale. In the latter case some of these new short-lived particles could be produced and detected at the LHC.

hep-ph↗

arXiv2008

A simple 5D SO(10) GUT and sparticle masses

Simple supersymmetric SO(10) GUT in five dimensions is proposed, in which the fifth dimension is compactified on the $S^1/(Z_2\times Z_2^\prime)$ orbifold with two inequivalent branes at the orbifold fixed points. In this model, all matter and Higgs multiplets reside on one brane (PS brane) where the Pati-Salam (PS) symmetry is manifest, while only the SO(10) gauge multiplet resides on the bulk. The supersymmetry breaking on the other brane (SO(10) brane) is transmitted to the PS brane through the gaugino mediation with the bulk gauge multiplet. We examine sparticle mass spectrum in this setup and show that the neutralino LSP as the dark matter candidate can be realized when the compactification scale of the fifth dimension is higher than the PS symmetry breaking scale, keeping the successful gauge coupling unification after incorporating threshold corrections of Kaluza-Klein modes of the bulk gauge multiplets.

hep-ph↗

arXiv2008

$ν$-GMSB with Type III Seesaw and Phenomenology

We show that when the supersymmetric SU(5) model is extended to explain small neutrino masses by the type III seesaw mechanism, the new {\bf 24}-dimensional fields needed for the purpose can act as messengers for transmitting SUSY breaking from a hidden sector to the visible sector. For the three {\bf 24} case, the constraints of grand unification and suppressed lepton flavor violation restrict the seesaw scale in this case to be in the narrow range of $10^{12}-10^{13}$ GeV. The model predicts (i) a stable LSP gravitino with mass in the range of 1-10 MeV which can be a cold dark matter of the universe; (ii) a stau NLSP which is detectable at LHC; (iii) a lower bound on the branching ratio $BR(μ\to e γ)$ larger than $10^{-14}$ testable by the ongoing MEG experiment as well as characteristic particle spectrum different from other SUSY breaking scenarios. We also discuss the case with two {\bf 24} fields, which is the minimal case that can explain neutrino oscillation data.

hep-ph↗

arXiv2008

Meta-stable Supersymmetry Breaking in an N=1 Perturbed Seiberg-Witten Theory

In this contribution, we discuss the possibility of meta-stable supersymmetry (SUSY) breaking vacua in a perturbed Seiberg-Witten theory with Fayet-Iliopoulos (FI) term. We found meta-stable SUSY breaking vacua at the degenerated dyon and monopole singular points in the moduli space at the nonperturbative level.

hep-th↗

arXiv2008

Realistic Hybrid Inflation in 5D Orbifold SO(10) GUT

We discuss the smooth hybrid inflation scenario in the context of a simple supersymmetric SO(10) GUT in 5D orbifold. In this GUT model, the SO(10) gauge symmetry is broken down to the Pati-Salam (PS) gauge group, SU(4)$_c \times$ SU(2)$_L \times$ SU(2)$_R$, by orbifold boundary conditions and all matter and Higgs multiplets are placed only on the brane (PS brane) where only the PS symmetry is manifest. Further breaking of the Pati-Salam group to the Standard Model one is realized by VEVs of the Higgs multiplets $({\bf 4},{\bf 1},{\bf 2}) \oplus (\overline{\bf 4},{\bf 1},{\bf 2})$. The gauge coupling unification is successfully realized at $M_{\rm GUT} =4.6 \times 10^{17}$ GeV after incorporating the threshold corrections of the Kaluza-Klein modes, with the compactification scale (assumed to be the same as the PS symmetry breaking scale) $M_c = v_{\rm PS}= 1.2 \times 10^{16}$ GeV. We show that this orbifold GUT model can naturally leads us to the smooth hybrid inflation, which tunes out to be consistent with the WMAP 5-year data with the predicted $M_{\rm GUT}$ and $v_{PS}$ in the model.

hep-ph↗

arXiv2008

Hidden particle production at the ILC

In a class of new physics models, new physics sector is completely or partly hidden, namely, singlet under the Standard Model (SM) gauge group. Hidden fields included in such new physics models communicate with the Standard Model sector through higher dimensional operators. If a cutoff lies in the TeV range, such hidden fields can be produced at future colliders. We consider a scalar filed as an example of the hidden fields. Collider phenomenology on this hidden scalar is similar to that of the SM Higgs boson, but there are several features quite different from those of the Higgs boson. We investigate productions of the hidden scalar at the International Linear Collider (ILC) and study the feasibility of its measurements, in particular, how well the ILC distinguishes the scalar from the Higgs boson, through realistic Monte Carlo simulations.

hep-ex↗