Publications (24)89.03 Total impact
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ABSTRACT: A novel model of spontaneous Leptogenesis is investigated, where it takes place in the thermal equilibrium due to a background NambuGoldstone field in motion. In particular, we identify the NambuGoldstone field to be the Majoron which associates with spontaneous breakdown of (discrete) $BL$ symmetry. In this scenario sufficient lepton number asymmetry is generated in primordial thermal bath without having $CP$violating outofequilibrium decay of the heavy righthanded Majorana neutrinos. To obtain the observed baryon asymmetry, the neutrino masses are predicted in certain ranges, which can be translated into the effective mass of the neutrinoless double beta decay. 
Article: Coupling Unification and Dark Matter in a Standard Model Extension with Adjoint Majorana Fermions
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ABSTRACT: We revisit an extension of the Standard Model with Majorana fermions in the adjoint representations. There, a precise coupling unification and the good candidate for dark matter (the $SU(2)_L$ triplet fermion) are achieved simultaneously. In particular, we show that the $SU(3)_c$ octet fermion which is required for successful unification can be a good nonthermal source of the triplet fermion dark matter. We also show that the scenario predicts a rather short lifetime of the proton compared with the supersymmetric Standard Model, and the most parameter space can be explored by the future experiments such as the HyperKamiokande experiment.  [Show abstract] [Hide abstract]
ABSTRACT: Composite Higgs models are an intriguing scenario in which the Higgs particle is identified as a pseudo NambuGoldstone boson associated with spontaneous breaking of some global symmetry above the electroweak scale. In general, such models predict new resonances at high energy scales, some of which can appear at multiTeV scales. In such a case, analogies with pion physics in QCD that a sizable phase shift is predicted in pionpion scattering processes might help us to evaluate scales of the resonances. In this paper, we discuss two complementary approaches to investigate the compositeness scale in minimal composite Higgs models. First, we discuss the bound on vector boson scattering from perturbative unitarity, and we evaluate the phase shift of the scattering amplitude. We obtain the relation between possible phase shifts and promising new resonance scales. We also investigate the possibility to measure the phase shift at LHC and the future hadron colliders. Second, we classify deviations in Higgs coupling constants from the standard model predictions in various kinds of the minimal composite Higgs models. We then discuss a possibility to discriminate a specific minimal composite Higgs model from the other models with extended Higgs sectors by utilizing deviation patterns in the Higgs boson couplings by future precision measurements.  [Show abstract] [Hide abstract]
ABSTRACT: We investigate gravitational effects on socalled multiple point criticality principle (MPCP) at the Planck scale. The MPCP requires two degenerate vacua, whose necessary conditions are expressed by vanishing Higgs quartic coupling ($\lambda(M_{\rm Pl})=0$) and vanishing its $\beta$function ($\beta_\lambda(M_{\rm Pl})=0$). In order to satisfy the conditions, we find that the top pole mass and the Higgs mass should be $170.8\,{\rm GeV} \lesssim M_t\lesssim 171.7\, {\rm GeV}$ and $M_h=125.7\pm0.4\, {\rm GeV}$, respectively, as well as suitable magnitude of gravitational effects (a coefficient of gravitational contribution as $a_\lambda > 2$). In this case, however, since the Higgs quartic coupling $\lambda$ becomes negative below the Planck scale, two vacua are not degenerate. We find that $M_h \gtrsim 131.5\, {\rm GeV}$ with $M_t \gtrsim 174\, {\rm GeV}$ is required by the realization of the MPCP. Therefore, the MPCP at the Planck scale cannot be realized in the SM and also the SM with gravity since $M_h \gtrsim 131.5\, {\rm GeV}$ is experimentally ruled out.  [Show abstract] [Hide abstract]
ABSTRACT: The observed neutrino flux can be as a whole well fitted by a simple powerlaw of the neutrino energy $E_\nu$, $E_\nu^{\gamma_\nu}$ ($\gamma_\nu \simeq 2$). As a notable feature of the spectrum, however, it has a gap between 500 TeV and 1 PeV. Although the existence of the gap in the neutrino spectrum is not statistically significant at this point, it is very enticing to ask whether it might hint some physics beyond the Standard Model. In this paper, we investigate a possibility that the gap can be interpreted as an absorption line in the powerlaw spectrum by the cosmic neutrino background through a new resonance in the MeV range. We also show that the absorption line has rich information about not only the MeV scale new particle but also the neutrino masses as well as the distances to the astrophysical sources of the high energy neutrinos. Viable models to achieve this possibility are also discussed.  [Show abstract] [Hide abstract]
ABSTRACT: We discuss the realization of a vanishing Higgs potential at the Planck scale, which is required by the multiple point criticality principle, in the standard model with singlet scalar dark matter and a righthanded neutrino. We find the scalar dark matter and the righthanded neutrino play crucial roles, and their masses, $m_S$ and $M_R$, must be $8.0\times10^2~{\rm GeV}\leq m_S\leq1.2\times10^3~{\rm GeV}$ and $6.3\times10^{13}~{\rm GeV}\leq M_R\leq1.6\times10^{14}~{\rm GeV}$ within current experimental values of the Higgs and top masses. This scenario is consistent with current dark matter direct search experiments, and will be confirmed by future experiments such as LUX with further exposure and/or XENON1T. 
Article: Next to new minimal standard model
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ABSTRACT: We suggest a minimal extension of the standard model, which can explain current experimental data of the dark matter, small neutrino masses and baryon asymmetry of the universe, inflation, and dark energy, and achieve gauge coupling unification. The gauge coupling unification can explain the charge quantization, and be realized by introducing six new fields. We investigate the vacuum stability, coupling perturbativity, and correct dark matter abundance in this model by use of current experimental data.  [Show abstract] [Hide abstract]
ABSTRACT: The large value of the tensortoscalar ratio in the cosmic microwave background radiation reported by the BICEP2 collaboration gives strong impact on models of supersymmetry (SUSY). The large ratio indicates inflation with a highenergy scale and thus a high reheating temperature in general, and various SUSY models suffer from the serious gravitino and Polonyi problems. In this article, we discuss a class of the highscale SUSY breaking models which are completely free from those problems. With especially focusing on the dark matter relic abundance, we examine how the BICEP2 result narrows down the parameter space of the models, assuming the simplest chaotic inflation model. We find that the mass of the dark matter is predicted to be less than about 1 TeV thanks to the nonthermal production in the early universe through the decay of abundant gravitinos produced after the reheating process. We also discuss implications in some details to dark matter searches at collider and indirect dark matter detection experiments. 
Article: Gaugino coannihilations
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ABSTRACT: The highscale supersymmetry (SUSY) breaking scenario is now attracting many attentions, because it is consistent with almost all experiments of particle physics, astrophysics, and cosmology performed so far: e.g. it is possible to explain the Higgs mass of about 126GeV and contains WIMP dark matter candidates. In the scenario, gauginos are predicted to be around the TeV scale, and thus within a kinematically accessible range of near future experiments. Calculation of the thermal relic abundance for gaugino (bino or wino) dark matter is then of particular importance in order to clarify its mass consistent with cosmology and to determine future directions for exploring the highscale SUSY breaking scenario. In this article, we calculate the abundance of the gaugino dark matter, with especially focusing on various coannihilations between gauginos, which has not been extensively studied so far. Our calculation involves the Sommerfeld effect on wino and gluino annihilations, which is known to give significant contributions to their cross sections. Based on obtained results, we discuss some implications to gaugino searches at collider and indirect detection experiments of dark matter.  [Show abstract] [Hide abstract]
ABSTRACT: We investigate accurate renormalization group analyses in neutrino sector between $\nu$oscillation and seesaw energy scales. We consider decoupling effects of top quark and Higgs boson on the renormalization group equations of light neutrino mass matrix. Since the decoupling effects are given in the standard model scale and independent of high energy physics, our method can basically apply to any models beyond the standard model. We find that the decoupling effects of Higgs boson are negligible, while those of top quark are not. Particularly, the decoupling effects of top quark affect neutrino mass eigenvalues, which are important for analyzing predictions such as mass squared differences and neutrinoless double beta decay in an underlying theory existing at high energy scale. 
Article: NNMSM typeII and III
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ABSTRACT: We suggest two types of extension of the standard model, which are the socalled next to new minimal standard model typeII and III. They can achieve gauge coupling unification as well as suitable dark matter abundance, small neutrino masses, baryon asymmetry of the universe, inflation, and dark energy. The gauge coupling unification can be realized by introducing two or three extra new fields, and they could explain charge quantization. We also show that there are regions in which the vacuum stability, coupling perturbativity, and correct dark matter abundance can be realized with current experimental data at the same time.  [Show abstract] [Hide abstract]
ABSTRACT: We investigate Planck scale boundary conditions on the Higgs sector of the standard model with a gauge singlet scalar dark matter. We will find that vanishing selfcoupling and Veltman condition at the Planck scale are realized with the 126 GeV Higgs mass and top pole mass, 171.8 GeV $\lesssim M_t\lesssim$ 173.5 GeV, where a correct abundance of scalar dark matter is obtained with mass of 300 GeV $\lesssim m_S \lesssim$ 1 TeV. It means that the Higgs potential is flat at the Planck scale, and this situation can not be realized in the standard model with the top pole mass.  [Show abstract] [Hide abstract]
ABSTRACT: Higgs cubic coupling plays a crucial role to probe an origin of electroweak symmetry breaking. It is expected that the cubic coupling is measured by Higgs pair production at the LHC and ILC, and the deviations from the standard model can be extracted from the Higgs pair production process, and those can give us a hint of new physics beyond the standard model. We consider a general potential that achieves the suitable electroweak symmetry breaking. As one of the interesting models, we suggest a nonperturbative Higgs model in which a runaway type of potential is used. In the model, the cross sections of pair production at the LHC is enlarged compared to the standard model. We also study the Higgs pair production induced by a noncanonical kinetic term of Higgs fields which will be important to search the pairproduction at the ILC. 
Article: NNMSM TypeII and III
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ABSTRACT: We suggests two types of extension of the standard model, which are socalled next to new minimal standard model (NNMSM) typeII and III. They can achieve gauge coupling unification as well as suitable dark matter abundance, small neutrino masses, baryon asymmetry of the universe, inflation, and dark energy. The gauge coupling unification can be realized by introducing extra two or three new fields, and could explain the charge quantization. We also show that there are regions in which the vacuum stability, coupling perturbativity, and correct dark matter abundance can be realized with current experimental data at the same time.  [Show abstract] [Hide abstract]
ABSTRACT: Extra dimension is one of the most attractive candidates beyond the Standard Model. In warped extra dimensional spacetime, not only gauge hierarchy problem but also quarklepton mass hierarchy can be naturally explained. In this setup, a sizable parity violation through KaluzaKlein gluon exchange appears in QCD process such as helicity dependent top pair production. We investigate this QCD parity violating process by use of $SO(5) \times U(1)$ gaugeHiggs unification model. We evaluate LHC observable quantities, i.e., a charge asymmetry and a forwardbackward asymmetry of the top pair production, and find that a sizable charge asymmetry can be observed with specific model parameters.  [Show abstract] [Hide abstract]
ABSTRACT: We investigate a stability of leptonic selfcomplementarity such that sum of three mixing angles in lepton sector is 90 degrees. Renormalization group equations in a context of minimal supersymmetric standard model for the selfcomplementarity are analyzed. It is seen that one of Majorana phases plays an important role for the stability of selfcomplementarity. We find some stable solutions against quantum corrections at a low energy. An effective neutrino mass for neutrinoless double beta decay is also evaluated by the use of neutrino parameters giving rise to the stable solutions.  [Show abstract] [Hide abstract]
ABSTRACT: Among three typical energy scales, a neutrino mass scale (m{sub {nu}}{approx}0.1eV), a GUT scale (M{sub GUT}{approx}10{sup 16}GeV), and a TeVscale (M{sub NP}{approx}1TeV), there is a fascinating relation of M{sub NP} AsymptoticallyEqualTo {radical}(m{sub {nu}} DotOperator M{sub GUT}) The TeVscale, M{sub NP}, is a new physics scale beyond the standard model which is regarded as 'supersymmetry' (SUSY) in this letter. We investigate phenomenology of SUSY SU(5) GUT with neutrinophilic Higgs, which realizes the above relation dynamically as well as the suitable magnitude of Dirac mass, m{sub {nu}}, through a tiny vacuum expectation value of neutrinophilic Higgs. As a remarkable feature of this model, accurate gauge coupling unification can be achieved as keeping with a proton stability. We also evaluate flavor changing processes in quark/lepton sectors.  [Show abstract] [Hide abstract]
ABSTRACT: We investigate a possibility if a loop diagram via Higgsino can enhance the Higgs to diphoton decay width in supersymmetric models with an extension of Higgs sector. A model with an additional nonrenormalizable term of Higgs fields is firstly analyzed where the higher order term can introduce the Higgs coupling to Higgsinos as well as charged Higgs bosons. We point out that a choice of the Higgs coupling to obtain a significant size of enhancement of diphoton decay width reduces the Higgs mass and/or a size of nonrenormalizable term needs to be large and a cutoff scale is around the weak scale. Another model in which the Higgsino mass term is generated by a nonperturbative instanton effect via a strong dynamics in a context of SUSY QCD is also suggested. It is shown that the sign of the Higgs coupling to fermions is opposite from perturbative models due to an operator including bosonic fields in the denominator and a constructive contribution to the diphoton decay amplitude can be easily obtained in this kind of model.  [Show abstract] [Hide abstract]
ABSTRACT: Among three typical energy scales, a neutrino mass scale (mν∼0.1 eV), a grand unified theory (GUT) scale (MGUT∼1016 GeV), and a TeV scale (MNP∼1 TeV), there is the fascinating relation of MNP≃√mν·MGUT. The TeV scale, MNP, is a new physics scale beyond the standard model which is regarded as “supersymmetry” in this article. We investigate the phenomenology of the supersymmetry SU(5) GUT with neutrinophilic Higgs, where the above relation is realized dynamically when neutrinos are Dirac particles. As a remarkable feature of this model, accurate gauge coupling unification can be achieved in keeping with a proton stability. We also evaluate flavor changing processes in quark/lepton sectors.  [Show abstract] [Hide abstract]
ABSTRACT: We suggest natural TeVscale seesaw with nonnegligible leftright neutrino mixings as preserving tiny neutrino masses. Our analysis is exhibited, without loss of generality, by taking a basis of the neutrino matrices, in which the condition to obtain the leftright mixings is clear. We also suggest a flavor symmetry as an underlying theory, which naturally realizes our setup to preserve tiny neutrino masses. Our setup can predict a magnitude of sin theta_13 in a region of 0.10 to 0.20, depending on the deviation from maximal atmospheric neutrino mixing and CP phase. We also investigate experimental constraints and phenomenology in our setup.
Publication Stats
139  Citations  
89.03  Total Impact Points  
Top Journals
Institutions

20132015

The University of Tokyo
白山, Tōkyō, Japan 
Mongolian Academy of Sciences
Улаанбаатар, Ulaanbaatar, Mongolia


20122014

Hokkaido University
 Division of Physics
Sapporo, Hokkaidō, Japan


20112012

Osaka University
 Department of Physics
Ibaraki, Osakafu, Japan
