Sapporo, Japan

Hokkai Gakuen University

hgu.jp
Sapporo, Japan

Hokkai Gakuen University is a private university in Sapporo, Hokkaidō, Japan. The precursor of the school was founded in 1885, and it was chartered as a university in 1952. Wikipedia.

SEARCH FILTERS
Time filter
Source Type

Hirata Y.,Hokkai Gakuen University
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2017

This paper outlines research conducted into what Japanese undergraduate students think about utilization of commercial online courseware in a blended language learning course; I also demonstrate apparent benefits and problems with introducing courseware in Japanese educational settings. A brief introduction of the concepts of CALL and availability of ICT in Japan is provided, followed by a short description of English language teaching in Japanese educational settings. The present study and its results are then explained. The findings show that different students had different opinions of the effectiveness of the courseware – less than half of them appreciated the benefits of the courseware, while the rest raised computer-related problems with learning English through it. It is crucial for teachers to determine how to construct face-to-face learning environments in order to accommodate students’ different demands and requests in blended learning classrooms. © Springer International Publishing AG 2017.


Choi K.-Y.,Asia Pacific Center for Theoretical Physics | Choi K.-Y.,Pohang University of Science and Technology | Seto O.,Hokkai Gakuen University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We show that a Dirac right-handed scalar neutrino can be dark matter (DM) as a weakly interacting massive particle in the neutrinophilic Higgs model. When the additional Higgs fields couple only to the leptonic sector through neutrino Yukawa couplings, the right number of relic density of DM can be obtained from thermal freeze-out of the DM annihilation into charged leptons and neutrinos. At present epoch, this tree-level annihilation into fermions is suppressed by the velocity of DM, and the one-loop annihilation cross section into γγ can be dominant because relevant coupling constants are different. Hence, the recently observed (tentative) gamma-ray line signal in the Fermi-Large Area Telescope can be naturally explained by the annihilation of right-handed sneutrino DM. © 2012 American Physical Society.


Okada N.,University of Alabama | Seto O.,Hokkai Gakuen University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

The isospin violating dark matter (IVDM) scenario offers an interesting possibility to reconcile conflicting results among direct dark matter search experiments for a mass range around 10 GeV. We consider two simple renormalizable IVDM models with a complex scalar dark matter and a Dirac fermion dark matter, respectively, whose stability is ensured by the conservation of "dark matter number." Although both models successfully work as the IVDM scenario with destructive interference between effective couplings to proton and neutron, the dark matter annihilation cross section is found to exceed the cosmological/astrophysical upper bounds. Then, we propose a simple scenario to reconcile the IVDM scenario with the cosmological/astrophysical bounds, namely, the IVDM being asymmetric. Assuming a suitable amount of dark matter asymmetry has been generated in the early Universe, the annihilation cross section beyond the cosmological/astrophysical upper bound nicely works to dramatically reduce the antidark matter relic density and as a result, the constraints from dark matter indirect searches are avoided. We also discuss collider experimental constraints on the models and an implication to Higgs boson physics. © 2013 American Physical Society.


Okada N.,University of Alabama | Seto O.,Hokkai Gakuen University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We propose a scenario with a fermion dark matter, where the dark matter particle used to be the Dirac fermion, but it takes the form of the Majorana fermion at a late time. The relic number density of the dark matter is determined by the dark matter asymmetry generated through the same mechanism as leptogenesis when the dark matter was the Dirac fermion. After efficient dark matter annihilation processes have frozen-out, a phase transition of a scalar field takes place and generates Majorana mass terms to turn the dark matter particle into the Majorana fermion. In order to address this scenario in detail, we propose two simple models. The first one is based on the Standard Model (SM) gauge group and the dark matter originates the SU(2) L doublet Dirac fermion, analogous to the Higgsino-like neutralino in supersymmetric models. We estimate the spin-independent/dependent elastic scattering cross sections of this late-time Majorana dark matter with a proton and find the possibility to discover it by the direct and/or indirect dark matter search experiments in the near future. The second model is based on the B-L gauged extension of the SM, where the dark matter is a SM singlet. Although this model is similar to the so-called Higgs portal dark matter scenario, the spin-independent elastic scattering cross section can be large enough to detect this dark matter in future experiments. © 2012 American Physical Society.


Okada N.,University of Alabama | Seto O.,Hokkai Gakuen University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

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 the Higgs portal dark matter model. We show that the thermal relic abundance of the right-handed neutrino dark matter with the 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. © 2010 The American Physical Society.


Okada N.,University of Alabama | Seto O.,Hokkai Gakuen University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

It has been recently pointed out that the excess of the gamma ray spectrum in the Fermi bubbles at low latitude can be well explained by the annihilation of dark matter particles. The best-fit candidate corresponds to the annihilation of a dark matter with mass of around 62 GeV into bb̄ with the cross section, σvâ‰3.3×10-26 cm3/s, or the annihilation of a dark matter with mass of around 10 GeV into a tau lepton pair with the cross section, σvâ‰5.6×10-27 cm3/s. We point out that the Higgs portal dark matter models are perfectly compatible with this interpretation of the dark matter annihilation, satisfying other phenomenological constraints. We also show that the parameter region which reproduces the best-fit values can be partly explored by the future direct dark matter search at the XENON1T. © 2014 American Physical Society.


Okada N.,University of Alabama | Seto O.,Hokkai Gakuen University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

We consider a simple extension of the type-II two-Higgs-doublet model by introducing a real scalar as a candidate for dark matter in the present Universe. The main annihilation mode of the dark matter particle with a mass of around 31-40 GeV is into a bb¯ pair, and this annihilation mode suitably explains the observed excess of the gamma-ray flux from the Galactic Center. We identify the parameter region of the model that can fit the gamma-ray excess and satisfy phenomenological constraints, such as the observed dark matter relic density and the null results of direct dark matter search experiments. Most of the parameter region is found to be within the search reach of future direct dark matter detection experiments. © 2014 American Physical Society.


Seto O.,Hokkai Gakuen University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

We show that the standard model (SM)-like Higgs boson may decay into neutrinos with a sizable decay branching ratio in one well-known two Higgs doublet model, so-called neutrinophilic Higgs model. This could happen if the mass of the lighter extra neutral Higgs boson is smaller than one half of the SM-like Higgs boson mass. The definite prediction of this scenario is that the rate of the SM-like Higgs boson decay into diphoton normalized by the SM value is about 0.9. In the case that a neutrino is Majorana particle, a displaced vertex of right-handed neutrino decay would be additionally observed. This example indicates that a large invisible Higgs boson decay could be irrelevant to dark matter. © 2015 American Physical Society.


Choi K.-Y.,Korea Astronomy and Space Science Institute | Seto O.,Hokkai Gakuen University
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2014

We consider axino warm dark matter in a supersymmetric axion model with R-parity violation. In this scenario, axino with the mass ma~≃7keV can decay into photon and neutrino resulting in the X-ray line signal at 3.5 keV, which might be the origin of unidentified X-ray emissions from galaxy clusters and Andromeda galaxy detected by the XMM-Newton X-ray observatory. © 2014 Elsevier B.V.


Kobayashi T.,Hokkaido University | Seto O.,Hokkai Gakuen University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

Large field inflation models are favored by the recent BICEP2 that has detected gravitational wave modes generated during inflation. We study general large field inflation models for which the potential contains (constant) quadratic and quartic terms of inflaton field. We show, in this framework, those inflation models can generate the fluctuation with the tensor-to-scalar ratio of 0.2 as well as the scalar spectral index of 0.96; those are very close to the center value of the tensor-to-scalar ratio reported by BICEP2 as well as Planck. Finally, we briefly discuss the particle physics model building of inflation. © 2014 American Physical Society.

Loading Hokkai Gakuen University collaborators
Loading Hokkai Gakuen University collaborators