2021/05/15 更新

写真a

アサカ タケヒコ
淺賀 岳彦
ASAKA Takehiko
所属
教育研究院 自然科学系 数理物質科学系列 教授
理学部 理学科 教授
職名
教授
外部リンク

学位

  • 博士 (理学) ( 1997年3月   東北大学 )

研究キーワード

  • 素粒子理論

研究分野

  • 自然科学一般 / 素粒子、原子核、宇宙線、宇宙物理にする理論

経歴(researchmap)

  • 新潟大学   自然科学研究科 数理物質科学専攻   教授

    2019年4月 - 現在

      詳細を見る

  • 新潟大学   理学部 理学科   教授

    2019年4月 - 現在

      詳細を見る

  • 新潟大学   理学部 理学科   准教授

    2017年4月 - 2019年3月

      詳細を見る

  • 新潟大学   自然科学研究科 数理物質科学専攻   准教授

    2010年4月 - 2019年3月

      詳細を見る

  • 新潟大学   理学部 物理学科 粒子科学   准教授

    2007年9月 - 2017年3月

      詳細を見る

  • スイス スイス連邦工科大学 ローザンヌ校(EFPL)   研究員

    2006年10月 - 2007年9月

      詳細を見る

  • 東北大学 大学院 理学研究科   研究員

    2005年9月 - 2006年9月

      詳細を見る

  • スイス スイス連邦工科大学 ローザンヌ校(EPFL)   研究員

    2003年10月 - 2005年8月

      詳細を見る

  • スイス ローザンヌ大学   研究員

    2002年9月 - 2003年9月

      詳細を見る

  • ドイツ ドイツ電子シンクロトロン研究所(DESY) 理論部   研究員

    2000年9月 - 2002年8月

      詳細を見る

  • 東京大学 大学院 理学系研究科   日本学術振興会特別研究員

    1999年4月 - 2000年8月

      詳細を見る

  • 東京大学 宇宙線研究所   研究員

    1997年4月 - 1999年3月

      詳細を見る

▶ 全件表示

経歴

  • 新潟大学   理学部 理学科   教授

    2019年4月 - 現在

  • 新潟大学   理学部 理学科   准教授

    2017年4月 - 2019年3月

  • 新潟大学   自然科学研究科 数理物質科学専攻   准教授

    2010年4月 - 2019年3月

  • 新潟大学   自然科学研究科 数理物質科学専攻   准教授

    2010年4月 - 2019年3月

  • 新潟大学   粒子科学   准教授

    2007年9月 - 2017年3月

学歴

  • 東北大学   Graduate School, Division of Natural Science   Department of Physics

    - 1997年3月

      詳細を見る

    国名: 日本国

    researchmap

 

論文

  • Hiding neutrinoless double beta decay in the minimal seesaw mechanism 査読

    Takehiko Asaka, Hiroyuki Ishida, Kazuki Tanaka

        2020年12月

     詳細を見る

    We present a possibility that the neutrinoless double beta decay can be
    hidden in the minimal seesaw mechanism where the standard model is extended by
    two right-handed neutrinos which have a hierarchical mass structure. In this
    framework, the lepton number is violated due to the massive Majorana neutrinos.
    Especially, we investigate the case that the heavier right-handed neutrino is
    sufficiently heavy to decouple from the decay while the lighter one is lighter
    enough than the typical Fermi-momentum scale of nuclei and gives a sizable
    contribution to the decay. Under the specific condition on mixing elements, the
    lighter right-handed neutrino can give a significant destructive contribution
    which suppresses or even hides to the effective mass of the neutrinoless double
    beta decay. In this case, the flavor structure of the mixing element of the
    lighter right-handed neutrino with ordinary neutrinos is predicted depending on
    the Majorana CP violating phase of active neutrinos.

    DOI: 10.1103/PhysRevD.103.015014

    researchmap

    その他リンク: http://arxiv.org/pdf/2012.12564v2

  • Lepton flavor model with modular $A_4$ symmetry in large volume limit 査読

    TAKEHIKO ASAKA, Yongtae Heo, Takahiro Yoshida

    Phys.Lett.B811   135956 - 135956   2020年12月

     詳細を見る

    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.physletb.2020.135956

    researchmap

  • Direct baryogenesis in the broken phase 査読

    Takehiko Asaka, Hiroyuki Ishida, Wen Yin

        2019年12月

     詳細を見る

    We show a new mechanism for baryogenesis where the reheating temperature can
    be smaller than the electroweak scale. The baryon number symmetry is violated
    by a dimension nine operator which conserves a baryon parity. A high energy
    quark from the decay of a heavy particle, e.g. inflaton, modulus or gravitino,
    undergoes flavor oscillation, and is thermalized due to the scatterings with
    the ambient thermal plasma. We point out that the baryon asymmetry of our
    universe can be generated due to the scatterings via the baryon number
    violating operator. Our scenario can be tested in neutron-antineutron
    oscillation experiments as well as other terrestrial experiments.

    DOI: 10.1007/JHEP07(2020)174

    researchmap

    その他リンク: http://arxiv.org/pdf/1912.08797v1

  • Modular $A_4$ invariance and leptogenesis 査読

    Takehiko Asaka, Yongtae Heo, Takuya H. Tatsuishi, Takahiro Yoshida

        2019年9月

     詳細を見る

    We consider a model with three right-handed neutrinos in which Yukawa
    coupling constants and Majorana masses are obtained by requiring the modular
    $A_4$ symmetry. It has been shown that the model can explain mass hierarchies
    and mixing patterns of charged leptons and neutrinos with the seesaw mechanism.
    In this article we investigate the leptogenesis by decays of right-handed
    neutrinos in this model. It is shown that masses of right-handed neutrinos are
    about $10^{13}$ GeV in order to account for the observed baryon asymmetry of
    the universe. Furthermore, the positive sign of the baryon asymmetry is
    obtained only for the limited ranges of mixing angles and CP violation phases
    of active neutrinos, which can be tested by future neutrino experiments.

    DOI: 10.1007/JHEP01(2020)144

    researchmap

    その他リンク: http://arxiv.org/pdf/1909.06520v1

  • Resonant leptogenesis at TeV-scale and neutrinoless double beta decay

    Takehiko Asaka, Takahiro Yoshida

        2018年12月

     詳細を見る

    担当区分:筆頭著者  

    We investigate a resonant leptogenesis scenario by quasi-degenerate
    right-handed neutrinos which have TeV-scale masses. Especially, we consider the
    case when two right-handed neutrinos are responsible to leptogenesis and the
    seesaw mechanism for active neutrino masses, and assume that the CP violation
    occurs only in the mixing matrix of active neutrinos. In this case the sign of
    the baryon asymmetry depends on the Dirac and Majorana CP phases as well as the
    mixing angle of the right-handed neutrinos. It is shown how the yield of the
    baryon asymmetry correlates with these parameters. In addition, we find that
    the effective neutrino mass in the neutrinoless double beta decay receives an
    additional constraint in order to account for the observed baryon asymmetry
    depending on the masses and mixing angle of right-handed neutrinos.

    DOI: 10.1007/JHEP09(2019)089

    researchmap

    その他リンク: http://arxiv.org/pdf/1812.11323v3

  • Tomography by neutrino pair beam 査読

    TAKEHIKO ASAKA, Okui, Hisashi, Tanaka, Minoru, Yoshimura, Motohiko

    Phys.Lett.B785   536 - 542   2018年10月

     詳細を見る

    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.physletb.2018.09.004

    Web of Science

    researchmap

  • Initial condition for baryogenesis via neutrino oscillation 査読

    Takehiko Asaka, Shintaro Eijima, Hiroyuki Ishida, Kosuke Minogawa, Tomoya Yoshii

    PHYSICAL REVIEW D96 ( 8 )   2017年10月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER PHYSICAL SOC  

    We consider a baryogenesis scenario via the oscillation of right-handed neutrinos with Majorana masses of the order of GeV, which are also responsible for neutrino masses by the seesaw mechanism. We study how the initial condition alters the prediction of the present baryon asymmetry by this mechanism. It is usually assumed that the abundance of right-handed neutrinos is zero after the reheating of the inflationary universe and they are produced in scattering processes by the renomalizable Yukawa interaction. However, the higher-dimensional operator with right-handed neutrinos may provide an additional production which is most effective at the reheating epoch. It is shown that such an initial abundance of right-handed neutrinos can significantly modify the prediction when the strong washout of the asymmetry is absent. This leads to the parameter space of the model for the successful baryogenesis being enlarged.

    DOI: 10.1103/PhysRevD.96.083010

    Web of Science

    researchmap

  • Lepton number violation by heavy Majorana neutrino in $B$ decays 査読

    Asaka, Takehiko, Hiroyuki Ishida

    Phys.Lett.B763   393 - 396   2016年12月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    Heavy Majorana neutrinos are predicted in addition to ordinary active neutrinos in the models with the seesaw mechanism. We investigate the lepton number violation (LNV) in B decays induced by such a heavy neutrino Nwith GeV- scale mass. Especially, we consider the decay channel B+ -> mu(+) N -> mu(+) mu(+) pi(-) and derive the sensitivity limits on the mixing angle Theta(mu) by the future search experiments at Belle II and in e(+) e(-) collisions at the Future Circular Collider (FCC-ee). (C) 2016 The Author(s). Published by Elsevier B.V.

    DOI: 10.1016/j.physletb.2016.10.070

    Web of Science

    researchmap

  • A facility to search for hidden particles at the CERN SPS: the SHiP physics case 査読

    Sergey Alekhin, Wolfgang Altmannshofer, Takehiko Asaka, Brian Batell, Fedor Bezrukov, Kyrylo Bondarenko, Alexey Boyarsky, Ki-Young Choi, Cristobal Corral, Nathaniel Craig, David Curtin, Sacha Davidson, Andre de Gouvea, Stefano Dell'Oro, Patrick deNiverville, P. S. Bhupal Dev, Herbi Dreiner, Marco Drewes, Shintaro Eijima, Rouven Essig, Anthony Fradette, Bjoern Garbrecht, Belen Gavela, Gian F. Giudice, Mark D. Goodsell, Dmitry Gorbunov, Stefania Gori, Christophe Grojean, Alberto Guffanti, Thomas Hambye, Steen H. Hansen, Juan Carlos Helo, Pilar Hernandez, Alejandro Ibarra, Artem Ivashko, Eder Izaguirre, Joerg Jaeckel, Yu Seon Jeong, Felix Kahlhoefer, Yonatan Kahn, Andrey Katz, Choong Sun Kim, Sergey Kovalenko, Gordan Krnjaic, Valery E. Lyubovitskij, Simone Marcocci, Matthew Mccullough, David McKeen, Guenakh Mitselmakher, Sven-Olaf Moch, Rabindra N. Mohapatra, David E. Morrissey, Maksym Ovchynnikov, Emmanuel Paschos, Apostolos Pilaftsis, Maxim Pospelov, Mary Hall Reno, Andreas Ringwald, Adam Ritz, Leszek Roszkowski, Valery Rubakov, Oleg Ruchayskiy, Ingo Schienbein, Daniel Schmeier, Kai Schmidt-Hoberg, Pedro Schwaller, Goran Senjanovic, Osamu Seto, Mikhail Shaposhnikov, Lesya Shchutska, Jessie Shelton, Robert Shrock, Brian Shuve, Michael Spannowsky, Andy Spray, Florian Staub, Daniel Stolarski, Matt Strassler, Vladimir Tello, Francesco Tramontano, Anurag Tripathi, Sean Tulin, Francesco Vissani, Martin W. Winkler, Kathryn M. Zurek

    REPORTS ON PROGRESS IN PHYSICS79 ( 12 )   2016年12月

     詳細を見る

    記述言語:英語   出版者・発行元:IOP PUBLISHING LTD  

    This paper describes the physics case for a new fixed target facility at CERN SPS. The SHiP (search for hidden particles) experiment is intended to hunt for new physics in the largely unexplored domain of very weakly interacting particles with masses below the Fermi scale, inaccessible to the LHC experiments, and to study tau neutrino physics. The same proton beam setup can be used later to look for decays of tau-leptons with lepton flavour number non-conservation, tau -> 3 mu and to search for weakly-interacting sub-GeV dark matter candidates. We discuss the evidence for physics beyond the standard model and describe interactions between new particles and four different portals-scalars, vectors, fermions or axion-like particles. We discuss motivations for different models, manifesting themselves via these interactions, and how they can be probed with the SHiP experiment and present several case studies. The prospects to search for relatively light SUSY and composite particles at SHiP are also discussed. We demonstrate that the SHiP experiment has a unique potential to discover new physics and can directly probe a number of solutions of beyond the standard model puzzles, such as neutrino masses, baryon asymmetry of the Universe, dark matter, and inflation.

    DOI: 10.1088/0034-4885/79/12/124201

    Web of Science

    researchmap

  • Reinterpretation of the Starobinsky model 査読

    Takehiko Asaka, Satoshi Iso, Hikaru Kawai, Kazunori Kohri, Toshifumi Noumi, Takahiro Terada

    PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS ( 12 )   2016年12月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:OXFORD UNIV PRESS INC  

    The Starobinsky model of inflation, consistent with Planck 2015, has a peculiar form of the action, which contains the leading Einstein term R, the R-2 term with a huge coefficient, and negligible higher-order terms. We propose an explanation of this form based on compactification of extra dimensions. Once tuning of order 10(-4) is accepted to suppress the linear term R, we no longer have to suppress higher-order terms, which give nontrivial corrections to the Starobinsky model. We show our predictions of the spectral index, its runnings, and the tensor-to-scalar ratio. Finally, we discuss a possibility that quantum gravity may appear at the scale Lambda greater than or similar to 5 x 10(15) GeV.

    DOI: 10.1093/ptep/ptw161

    Web of Science

    researchmap

  • On neutrinoless double beta decay in the $\nu$MSM 査読

    Asaka, Takehiko, Eijima, Shintaro, Hiroyuki Ishida

    Phys.Lett.B762   371 - 375   2016年11月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    We consider the neutrinoless double beta (0 nu beta beta) decay in the nu MSM, in which three right-handed neutrinos with masses below the electroweak scale are additionally introduced to the Standard Model. In this model there appear three heavy neutral leptons N-1, N-2, and N-3 corresponding to right-handed neutrinos. It has been known that the lightest one N-1 with keV mass, which is a candidate for dark matter, gives a negligible contribution to the 0 nu beta beta decay. By contrast, the heavier ones N-2 and N-3, which are responsible to the seesaw mechanism of neutrino masses and baryogenesis, give the destructive contribution (compared with one from active neutrinos). This is because their mass degeneracy at high precision has been assumed, which is expected by analytical studies of baryogenesis. In this analysis, we find that the effective mass of the 0 nu beta beta decay becomes larger than one from active neutrinos due to the N-2 and N-3 constructive contribution when the mass difference becomes larger and the mass ordering of active neutrinos is inverted. Such a possibility will be explored by the current and near future experiments of the 0 nu beta beta decay. (C) 2016 The Author(s). Published by Elsevier B.V.

    DOI: 10.1016/j.physletb.2016.09.044

    Web of Science

    researchmap

  • Basic oscillation measurables in the neutrino pair beam 査読

    Asaka, T., Tanaka, M., Yoshimura, M.

    Phys.Lett.B760   359 - 364   2016年9月

     詳細を見る

    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.physletb.2016.07.001

    researchmap

  • Probing heavy neutrinos in the COMET experiment 査読

    Asaka, Takehiko, Watanabe, Atsushi

    PTEP2016 ( 3 )   2016年3月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:OXFORD UNIV PRESS INC  

    We argue that the COMET experiment-a dedicated experiment for the mu-e conversion search-has a good potential to search for heavy neutrinos in the mass range 1 MeV less than or similar to M less than or similar to 100 MeV. The stopped muons captured by the target nuclei or decaying in orbit efficiently produce heavy neutrinos via the active-sterile mixing. The produced heavy neutrinos then decay to electronpositron pairs (plus an active neutrino), which charged particles hit the cylindrical drift chamber surrounding the target. If the backgrounds from gamma rays are sufficiently rejected by some method, the expected sensitivity becomes comparable to the PS191 bound when the COMET experiment achieves similar to 10(17) stopping muons in the target.

    DOI: 10.1093/ptep/ptw011

    Web of Science

    researchmap

  • Perturbativity in the seesaw mechanism 査読

    Asaka, Takehiko, Tsuyuki, Takanao

    Phys.Lett.B753   147 - 149   2016年2月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    We consider the Standard Model extended by right-handed neutrinos to explain massive neutrinos through the seesaw mechanism. The new fermion can be observed when it has a sufficiently small mass and large mixings to left-handed neutrinos. If such a particle is the lightest right-handed neutrino, its contribution to the mass matrix of active neutrinos needs to be canceled by that of a heavier one. Yukawa couplings of the heavier one are then larger than those of the lightest one. We show that the perturbativity condition gives a severe upper bound on the mixing of the lightest right-handed neutrino, depending on the masses of heavier ones. Models of high energy phenomena, such as leptogenesis, can be constrained by low energy experiments. (C) 2015 The Authors. Published by Elsevier B.V.

    DOI: 10.1016/j.physletb.2015.12.013

    Web of Science

    researchmap

  • Seesaw mechanism at electron-electron colliders 査読

    TAKEHIKO ASAKA, Tsuyuki, Takanao

    Phys.Rev.D92 ( 9 ) 094012 - 094012   2015年11月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Physical Society  

    We consider the Standard Model with right-handed neutrinos to explain the masses of active neutrinos by the seesaw mechanism. Since active neutrinos as well as heavy neutral leptons are Majorana fermions in this case, the lepton number violating process can be induced. We discuss the inverse neutrinoless double beta decay e-e-→W-W- in the framework of the seesaw mechanism and its detectability at future colliders. It is shown that the cross section can be 17 fb for s=3 TeV even with the stringent constraint from the neutrinoless double beta decays if three (or more) right-handed neutrinos exist. In such a case, the future e-e- colliders can test lepton number violation mediated by a right-handed neutrino lighter than about 10 TeV.

    DOI: 10.1103/PhysRevD.92.094012

    Scopus

    researchmap

  • Lepton Universality in the νMSM 査読

    Takehiko Asaka, Shintaro Eijima, Kazuhiro Takeda

    Physics Letters B742   303 - 309   2015年3月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.physletb.2015.01.049

    Web of Science

    researchmap

  • Lightest sterile neutrino abundance within the vMSM (vol 1, 091, 2007) 査読

    Takehiko Asaka, Mikhail Shaposhnikov, Mikko Laine

    JOURNAL OF HIGH ENERGY PHYSICS ( 2 )   2015年2月

     詳細を見る

    記述言語:英語   出版者・発行元:SPRINGER  

    DOI: 10.1007/JHEP02(2015)028

    Web of Science

    researchmap

  • Heavy neutrino search in accelerator-based experiments 査読

    Asaka, Takehiko, Eijima, Shintaro, Watanabe, Atsushi

    JHEP03 ( 3 ) 125 - 125   2013年12月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:SPRINGER  

    We explore the feasibility of detecting heavy neutrinos by the existing facilities of neutrino experiments. A heavy neutrino in the mass range 1 MeV less than or similar to M-N less than or similar to 500 MeV is produced by pion or kaon decay, and decays to charged particles which leave signals in neutrino detectors. Taking the T2K experiment as a typical example, we estimate the heavy neutrino flux produced in the neutrino beam line. Due to massive nature of the heavy neutrino, the spectrum of the heavy neutrino is significantly different from that of the ordinary neutrinos. While the ordinary neutrinos are emitted to various directions in the laboratory frame due to their tiny masses, the heavy neutrinos tend to be emitted to the forward directions and frequently hit the detector. The sensitivity for the mixing parameters is studied by evaluating the number of signal events in the near detector ND280. For the electron-type mixing, the sensitivity of T2K at 10(21) POT is found to be better than that of the previous experiment PS191, which has placed the most stringent bounds on the mixing, parameters of the heavy neutrinos for 140 MeV less than or similar to M-N less than or similar to 500 MeV.

    DOI: 10.1007/JHEP03(2013)125

    Web of Science

    researchmap

  • Direct Search for Right-handed Neutrinos and Neutrinoless Double Beta Decay 査読

    Asaka, Takehiko, Eijima, Shintaro

    PTEP2013 ( 11 )   2013年8月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Physical Society of Japan  

    We consider an extension of the Standard Model by two right-handed neutrinos, especially with masses lighter than the charged K meson. This simple model can realize the seesaw mechanism for neutrino masses and also baryogenesis by flavor oscillations of right-handed neutrinos. We summarize the constraints on right-handed neutrinos from direct searches as well as big bang nucleosynthesis. It is then found that the possible range for the quasi-degenerate mass of righthanded neutrinos is M&lt
    inf&gt
    N&lt
    /inf&gt
    ≥ 163MeV for the normal hierarchy of neutrino masses, while M&lt
    inf&gt
    N&lt
    /inf&gt
    = 188-269MeV and M&lt
    inf&gt
    N&lt
    /inf&gt
    ≥ 285MeV for the inverted hierarchy case. Furthermore, we find in the latter case that the possible value of the Majorana phase is restricted for M&lt
    inf&gt
    N&lt
    /inf&gt
    = 188-350 MeV, which leads to the fact that the rate of neutrinoless double beta decay is also limited.

    DOI: 10.1093/ptep/ptt094

    Scopus

    researchmap

  • Heavy neutrino search in accelerator-based experiments 査読

    Takehiko Asaka, Shintaro Eijima, Atsushi Watanabe

    Journal of High Energy Physics ( 11 )   2013年3月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1093/ptep/ptt094

    Web of Science

    researchmap

  • Kinetic Equations for Baryogenesis via Sterile Neutrino Oscillation 査読

    Asaka, Takehiko, Eijima, Shintaro, Ishida, Hiroyuki

    JCAP02 ( 2 ) 021 - 021   2012年12月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP PUBLISHING LTD  

    We investigate baryogenesis in the nu MSM (neutrino Minimal Standard Model), which is the SM extended by three right-handed neutrinos with masses below the electroweak scale. The baryon asymmetry of the universe can be generated by the mechanism via flavor oscillation of right-handed (sterile) neutrinos which are responsible to masses of active neutrinos confirmed by various experiments. We present the kinetic equations for the matrix of densities of leptons which describe the generation of asymmetries. Especially, the momentum dependence of the matrix of densities is taken into account. By solving these equations numerically, it is found that the momentum distribution is significantly distorted from the equilibrium one, since the production for the modes with lower momenta k << T (T is the temperature of the universe) is enhanced, while suppressed for higher modes. As a result, the most important mode for the yields of sterile neutrinos as well as the baryon asymmetry is k similar or equal to 2 T, which is smaller than < k > inferred from the thermal average. The comparison with the previous works is also discussed.

    DOI: 10.1088/1475-7516/2012/02/021

    Web of Science

    researchmap

  • Atmospheric Sterile Neutrinos 査読

    Asaka, Takehiko, Watanabe, Atsushi

    JHEP07 ( 7 ) 112 - 112   2012年2月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:SPRINGER  

    We study production of sterile neutrinos in the atmosphere and their detection at Super-Kamiokande. A sterile neutrino in the mass range 1 MeV less than or similar to M<INF>N</INF> less than or similar to 105 MeV is produced by muon or pion decay, and decays to an electron-positron pair and an active neutrino. Such a decay of the sterile neutrino leaves two electron-like Cherenkov rings in the detector. We estimate the sterile neutrino flux from the well-established active neutrino fluxes and study the number of the decay events in the detector. The upper bounds for the active-sterile mixings are obtained by comparing the 2e-like events from the sterile neutrino decays and the observed data by Super-Kamiokande. The upper bound for the muon type mixing Theta<INF>& is found to be vertical bar Theta<INF>&<SUP>2</SUP> less than or similar to 5 x 10<SUP>-5</SUP> for 20MeV less than or similar to M<INF>N</INF> less than or similar to 80MeV, which is significantly loosened compared to the previous estimation. We demonstrate that the opening angle and the total energy of the rings may serve as diagnostic tools to discover the sterile neutrinos in further data accumulation and future upgraded facilities. The directional asymmetry of the events is a sensitive measure of the diminishment of the sterile neutrino flux due to the decays on the way to the detector.

    DOI: 10.1007/JHEP07(2012)112

    Web of Science

    researchmap

  • Mixing of Active and Sterile Neutrinos 査読

    Asaka, Takehiko, Eijima, Shintaro, Ishida, Hiroyuki

    JHEP04 ( 4 ) 011 - 011   2011年1月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:SPRINGER  

    We investigate mixing of neutrinos in the vMSM (neutrino Minimal Standard Model), which is the MSM extended by three right-handed neutrinos. Especially, we study elements of the mixing matrix Theta(alpha I) between three left-handed neutrinos v(L alpha) (alpha = e, mu, tau) and two sterile neutrinos N-I (I = 2, 3) which are responsible to the seesaw mechanism generating the suppressed masses of active neutrinos as well as the generation of the baryon asymmetry of the universe. It is shown that Theta(eI) can be suppressed by many orders of magnitude compared with Theta(mu I) and Theta(tau I), when the Chooz angle theta(13) is large in the normal hierarchy of active neutrino masses. We then discuss the neutrinoless double beta decay in this framework by taking into account the contributions not only from active neutrinos but also from all the three sterile neutrinos. It is shown that N-2 and N-3 give substantial, destructive contributions when their masses are smaller than a few 100 MeV, and as a results Theta(eI) receive no stringent constraint from the bounds on such decays. Finally, we discuss the impacts of the obtained results on the direct searches of N-2,N-3 in meson decays for the case when N-2,N-3 are lighter than pion mass. We show that there exists the allowed region for N-2,N-3 with such small masses in the normal hierarchy case even if the current bound on the lifetimes of N-2,N-3 from the big bang nucleosynthesis is imposed. It is also pointed out that the direct search by using pi(+) -> e(+) + N-2,N-3 and K+ -> e(+) + N-2,N-3 might miss such N-2,N-3 since the branching ratios can be extremely small due to the cancellation in Theta(eI), but the search by K+ -> mu(+) + N-2,N-3 can cover the whole allowed region by improving the measurement of the branching ratio by a factor of 5.

    DOI: 10.1007/JHEP04(2011)011

    Web of Science

    researchmap

  • Flavour mixing of neutrinos and baryon asymmetry of the universe 査読

    Takehiko Asaka, Hiroyuki Ishida

    PHYSICS LETTERS B692 ( 2 ) 105 - 113   2010年8月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    We investigate baryogenesis in the nu MSM, which is the Minimal Standard Model (MSM) extended by three right-handed neutrinos with Majorana masses smaller than the weak scale. In this model the baryon asymmetry of the universe (BAU) is generated via flavour oscillation between right-handed neutrinos. We consider the case when BAU is solely originated from the CP violation in the mixing matrix of active neutrinos. We perform analytical and numerical estimations of the yield of BAU, and show how BAU depends on mixing angles and CP violating phases. It is found that the asymmetry in the inverted hierarchy for neutrino masses receives a suppression factor of about 4% comparing with the normal hierarchy case. It is, however, pointed out that, when theta(13) = 0 and theta(23) = pi/4, baryogenesis in the normal hierarchy becomes ineffective, and hence the inverted hierarchy case becomes significant to account for the present BAU. (C) 2010 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.physletb.2010.07.016

    Web of Science

    researchmap

  • Non-perturbative Corrections to Particle Production from Coherent Oscillation 査読

    Asaka, Takehiko, Nagao, Hiroaki

    Prog.Theor.Phys.124 ( 2 ) 293 - 314   2010年4月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE  

    We investigate particle production from coherent oscillation using the method based on the Bogolyubov transformation. In particular, we study the case when the amplitude of the oscillation and also the coupling constants with the oscillating field are small to avoid the nonperturbative corrections from the broad parametric resonance. We derive the expressions for the distribution functions and the number densities of produced particles at the leading order of coupling constant. It is, however, found that these results fail to describe the exact particle production eventually due to the nonperturbative effects even if the coupling constants are small. We then introduce a simple method of handling such corrections, i.e., the time averaging method. It is shown that this method can successfully provide the evolution of the occupation numbers of the growing mode. Furthermore, we point out that the approximate results obtained by this method satisfy the exact scaling properties coming from the periodicity of the coherent oscillation.

    DOI: 10.1143/PTP.124.293

    Web of Science

    researchmap

  • Flavour Mixing of Neutrinos and Baryon Asymmetry of the Universe 査読

    Asaka, Takehiko, Ishida, Hiroyuki

    Phys.Lett.B692 ( 2 ) 105 - 113   2010年4月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    We investigate baryogenesis in the nu MSM, which is the Minimal Standard Model (MSM) extended by three right-handed neutrinos with Majorana masses smaller than the weak scale. In this model the baryon asymmetry of the universe (BAU) is generated via flavour oscillation between right-handed neutrinos. We consider the case when BAU is solely originated from the CP violation in the mixing matrix of active neutrinos. We perform analytical and numerical estimations of the yield of BAU, and show how BAU depends on mixing angles and CP violating phases. It is found that the asymmetry in the inverted hierarchy for neutrino masses receives a suppression factor of about 4% comparing with the normal hierarchy case. It is, however, pointed out that, when theta(13) = 0 and theta(23) = pi/4, baryogenesis in the normal hierarchy becomes ineffective, and hence the inverted hierarchy case becomes significant to account for the present BAU. (C) 2010 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.physletb.2010.07.016

    Web of Science

    researchmap

  • Baryogenesis via Sterile neutrino oscillation and neutrino parameters 査読

    Takehiko Asaka, Hiroyuki Ishida

    PROGRESS IN PARTICLE AND NUCLEAR PHYSICS64 ( 2 ) 390 - 392   2010年4月

     詳細を見る

    記述言語:英語   出版者・発行元:ELSEVIER SCIENCE BV  

    We investigate baryogenesis in the nu MSM which is the Minimal Standard Model (MSM) extended by three right-handed neutrinos with Majorana masses being smaller than the weak scale. In this model three sterile neutrinos, which are almost right-handed states, play important roles in cosmology. The baryon asymmetry of the universe (BAU) is generated via mechanism through flavor oscillation between two sterile neutrinos N(2) and N(3) which are degenerate in masses. We consider the case when BAU is solely originated from the CP violating phases in the mixing matrix of active neutrinos, i.e., the Dirac phase delta and the Majorana phase eta, and study how BAU depends on these CP violating phases. (C) 2010 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.ppnp.2009.12.056

    Web of Science

    researchmap

  • Leptogenesis with an almost conserved lepton number 査読

    Asaka, Takehiko, Blanchet, Steve

    Phys.Rev.D78 ( 12 ) 123527 - 123527   2008年10月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER PHYSICAL SOC  

    Seesaw models with a slightly broken lepton number symmetry can explain small neutrino masses, and allow for low-scale leptogenesis. We make a thorough analysis of leptogenesis within the simplest model with two right-handed (RH) neutrinos (or with N(3) decoupled). We obtain a semianalytical formula for the final asymmetry in both supersymmetric and nonsupersymmetric cases with a simple dependence on each parameter. The low-energy parameters factorize from the high-energy ones, and the high-energy phase must be nonzero. The role of the low-energy phases is carefully studied. Moreover, we find that the breaking parameter in the Yukawa coupling matrix must be relatively large, epsilon(h)greater than or similar to 10(-3) for normal and 10(-2) for inverted hierarchy. Therefore, leptogenesis in our simple model is incompatible with RH neutrino signals at future colliders or sizable lepton-flavor violation. The other breaking parameter, epsilon(M), which appears in the RH neutrino mass matrix, can be much smaller, and actually needs to be so in order to have low-scale leptogenesis.

    DOI: 10.1103/PhysRevD.78.123527

    Web of Science

    researchmap

  • Right-handed sneutrino as cold dark matter of the universe 査読

    Takehiko Asaka

    TAUP2007: TENTH INTERNATIONAL CONFERENCE ON TOPICS IN ASTROPARTICLE AND UNDERGROUND PHYSICS120   2008年

     詳細を見る

    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IOP PUBLISHING LTD  

    We consider the minimal supersymmetric standard model (MSSM) extended by three right-handed neutrinos. Assuming that neutrino masses are purely Dirac-type, the lightest right-handed sneutrino (nu) over bar (R) can be the lightest superparticle (LSP). We discuss the possibility that the (nu) over bar (R) becomes dark matter of the universe, paying attention to the production of (nu) over bar (R) in the early universe. This work is based on collaboration with K. Ishiwata and T. Moroi [1, 2].

    DOI: 10.1088/1742-6596/120/4/042006

    Web of Science

    researchmap

  • Right-handed sneutrino as cold dark matter of the universe 査読

    Asaka, Takehiko, Ishiwata, Koji, Moroi, Takeo

    Phys.Rev.D75 ( 6 ) 065001 - 065001   2007年12月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMERICAN PHYSICAL SOC  

    We consider the minimal supersymmetric standard model (MSSM) extended by introducing three right-handed (s)neutrinos to account for neutrino masses in the oscillation experiments. Assuming that the neutrino masses are purely Dirac type, the lightest right-handed sneutrino nu(R) can be the lightest superparticle (LSP), which is a good candidate of cold dark matter (CDM) of the Universe. We study the possibility of realizing nu(R)-CDM, paying special attention to the production of nu(R) via decay of the next-to-lightest superparticle after its freeze-out time. It is shown that the late decay of the MSSM-LSP (the LSP among superparticles in the MSSM) can produce a sufficient amount of nu(R) to explain the observed dark matter density, and that the nu(R)-CDM scenario can be realized in a wide range of parameter space. We also consider the constraint on the decay of MSSM-LSP from the big bang nucleosynthesis; we found that the case with stau being the MSSM-LSP is severely constrained.

    DOI: 10.1103/PhysRevD.75.065001

    Web of Science

    researchmap

  • Lightest sterile neutrino abundance within the vMSM 査読

    Takehiko Asaka, Mikhail Shaposhnikov, Mikko Laine

    JOURNAL OF HIGH ENERGY PHYSICS ( 1 )   2007年1月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:SPRINGER  

    We determine the abundance of the lightest (dark matter) sterile neutrinos created in the Early Universe due to active-sterile neutrino transitions from the thermal plasma. Our starting point is the field-theoretic formula for the sterile neutrino production rate, derived in our previous work [JHEP 06( 2006) 053], which allows to systematically incorporate all relevant effects, and also to analyse various hadronic uncertainties. Our numerical results direr moderately from previous computations in the literature, and lead to an absolute upper bound on the mixing angles of the dark matter sterile neutrino. Comparing this bound with existing astrophysical X-ray constraints, we find that the Dodelson-Widrow scenario, which proposes sterile neutrinos generated by active-sterile neutrino transitions to be the sole source of dark matter, is only possible for sterile neutrino masses lighter than 3.5 keV (6 keV if all hadronic uncertainties are pushed in one direction and the most stringent X-ray bounds are relaxed by a factor of two). This upper bound may conflict with a lower bound from structure formation, but a definitive conclusion necessitates numerical simulations with the non-equilibrium momentum distribution function that we derive. If other production mechanisms are also operative, no upper bound on the sterile neutrino mass can be established.

    Web of Science

    researchmap

  • Lightest sterile neutrino abundance within the νMSM 査読

    Takehiko Asaka, Mikhail Shaposhnikov, Mikko Laine

    Journal of High Energy Physics2007 ( 1 ) 091   2007年1月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1088/1126-6708/2007/01/091

    Web of Science

    researchmap

  • Right-handed sneutrino as cold dark matter of the universe 査読

    Takehiko Asaka, Koji Ishiwata, Takeo Moroi

    SUSY06: THE 14TH INTERNATIONAL CONFERENCE ON SUPERSYMMETRY AND THE UNIFICATION OF FUNDAMENTAL INTERACTIONS903   16 - +   2007年

     詳細を見る

    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:AMER INST PHYSICS  

    In supersymmetric models with right-handed neutrinos where the neutrino masses are purely Dirac-type, right-handed sneutrino is an interesting candidate of the lightest superparticle (LSP). Here we discuss the possibility that right-handed-sneutrino-LSP becomes dark matter of the universe.

    Web of Science

    researchmap

  • Right-handed sneutrino as cold dark matter 査読

    Asaka, Takehiko, Ishiwata, Koji, Moroi, Takeo

    Phys.Rev.D73 ( 5 ) 051301 - 051301   2006年12月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMERICAN PHYSICAL SOC  

    We consider supersymmetric models with right-handed neutrinos where neutrino masses are purely Dirac-type. In this model, right-handed sneutrino can be the lightest supersymmetric particle and can be a viable candidate of cold dark matter of the universe. Right-handed sneutrinos are never thermalized in the early universe because of weakness of Yukawa interaction, but are effectively produced by decays of various superparticles. We show that the present mass density of right-handed sneutrino can be consistent with the observed dark matter density.

    DOI: 10.1103/PhysRevD.73.051301

    Web of Science

    researchmap

  • On the hadronic contribution to sterile neutrino production 査読

    Asaka, Takehiko, Laine, Mikko, Shaposhnikov, Mikhail

    JHEP06 ( 6 ) 053 - 053   2006年5月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:SPRINGER  

    Sterile neutrinos with masses in the keV range are considered to be a viable candidate for warm dark matter. The rate of their production through active-sterile neutrino transitions peaks, however, at temperatures of the order of the QCD scale, which makes it difficult to estimate their relic abundance quantitatively, even if the mass of the sterile neutrino and its mixing angle were known. We derive here a relation, valid to all orders in the strong coupling constant, which expresses the production rate in terms of the spectral function associated with active neutrinos. The latter can in turn be expressed as a certain convolution of the spectral functions related to various mesonic current-current correlation functions, which are being actively studied in other physics contexts. In the naive weak coupling limit, the appropriate Boltzmann equations can be derived from our general formulae.

    DOI: 10.1088/1126-6708/2006/06/053

    Web of Science

    researchmap

    その他リンク: http://weblib.cern.ch/abstract?CERN-PH-TH-2006-085

  • Gravitinos from heavy scalar decay 査読

    Asaka, Takehiko, Nakamura, Shuntaro, Yamaguchi, Masahiro

    Phys.Rev.D74 ( 2 ) 023520 - 023520   2006年4月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER PHYSICAL SOC  

    Cosmological issues of the gravitino production by the decay of a heavy scalar field X are examined, assuming that the damped coherent oscillation of the scalar once dominated the energy of the universe. The coupling of the scalar field to a gravitino pair is estimated both in spontaneous and explicit supersymmetry breaking scenarios, with the result that it is proportional to the vacuum expectation value of the scalar field in general. Cosmological constraints depend on whether the gravitino is stable or not, and we study each case separately. For the unstable gravitino with M-3/2 similar to 100 GeV-10 TeV, we obtain not only the upper bound, but also the lower bound on the reheating temperature after the X decay, in order to retain the success of the big-bang nucleosynthesis. It is also shown that it severely constrains the decay rate into the gravitino pair. For the stable gravitino, similar but less stringent bounds are obtained to escape the overclosure by the gravitinos produced at the X decay. The requirement that the free-streaming effect of such gravitinos should not suppress the cosmic structures at small scales eliminates some regions in the parameter space, but still opens a new window for the gravitino warm dark matter. Implications of these results to inflation models are discussed. In particular, it is shown that modular inflation will face serious cosmological difficulty when the gravitino is unstable, whereas it can escape the constraints for the stable gravitino. A similar argument offers a solution to the cosmological moduli problem, in which the moduli is relatively heavy while the gravitino is light.

    DOI: 10.1103/PhysRevD.74.023520

    Web of Science

    researchmap

  • Opening a new window for warm dark matter 査読

    Asaka, Takehiko, Shaposhnikov, Mikhail, Kusenko, Alexander

    Phys.Lett.B638 ( 5-6 ) 401 - 406   2006年2月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    We explore the range of parameters for dark-matter sterile neutrinos in an extension of the Minimal Standard Model by three singlet fermions with masses below the electroweak scale (the nu MSM). This simple model can explain a wide range of phenomena, including neutrino oscillations, baryogenesis. the pulsar velocities, and the early reionization. The presence of two heavier sterile neutrinos and the possibility of entropy production in their decays broadens the allowed range of parameters for the dark-matter sterile neutrinos (or other types of dark matter, for example, the gravitino). In addition, the primordial production of dark matter sterile neutrinos allows to escape most of the constraints. (c) 2006 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.physletb.2006.05.067

    Web of Science

    researchmap

  • Gravitinos from heavy scalar decay 査読

    Takehiko Asaka, Shuntaro Nakamura, Masahiro Yamaguchi

    Physical Review D - Particles, Fields, Gravitation and Cosmology74 ( 2 )   2006年

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    Cosmological issues of the gravitino production by the decay of a heavy scalar field X are examined, assuming that the damped coherent oscillation of the scalar once dominated the energy of the universe. The coupling of the scalar field to a gravitino pair is estimated both in spontaneous and explicit supersymmetry breaking scenarios, with the result that it is proportional to the vacuum expectation value of the scalar field in general. Cosmological constraints depend on whether the gravitino is stable or not, and we study each case separately. For the unstable gravitino with M3/2∼100GeV-10TeV, we obtain not only the upper bound, but also the lower bound on the reheating temperature after the X decay, in order to retain the success of the big-bang nucleosynthesis. It is also shown that it severely constrains the decay rate into the gravitino pair. For the stable gravitino, similar but less stringent bounds are obtained to escape the overclosure by the gravitinos produced at the X decay. The requirement that the free-streaming effect of such gravitinos should not suppress the cosmic structures at small scales eliminates some regions in the parameter space, but still opens a new window for the gravitino warm dark matter. Implications of these results to inflation models are discussed. In particular, it is shown that modular inflation will face serious cosmological difficulty when the gravitino is unstable, whereas it can escape the constraints for the stable gravitino. A similar argument offers a solution to the cosmological moduli problem, in which the moduli is relatively heavy while the gravitino is light. © 2006 The American Physical Society.

    DOI: 10.1103/PhysRevD.74.023520

    Scopus

    researchmap

  • The νMSM, dark matter and neutrino masses 査読

    Takehiko Asaka, Steve Blanchet, Mikhail Shaposhnikov

    Physics Letters B631 ( 4 ) 151 - 156   2005年12月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.physletb.2005.09.070

    Web of Science

    researchmap

  • The νMSM, dark matter and baryon asymmetry of the universe 査読

    Takehiko Asaka, Mikhail Shaposhnikov

    Physics Letters B620 ( 1-2 ) 17 - 26   2005年7月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.physletb.2005.06.020

    Web of Science

    researchmap

  • Late reheating, hadronic jets and baryogenesis 査読

    Asaka, Takehiko, Grigoriev, Dmitri, Kuzmin, Vadim, Shaposhnikov, Mikhail

    Phys.Rev.Lett.92 ( 10 ) 101303 - 101303   2004年10月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMERICAN PHYSICAL SOC  

    If inflaton couples very weakly to ordinary matter, the reheating temperature of the Universe can be lower than the electroweak scale. In this Letter we show that the late reheating occurs in a highly nonuniform way, within narrow areas along the jets produced by ordinary particles originated from inflaton decays. Depending on inflaton mass and decay constant, the initial temperature inside the lumps of the overheated plasma may be large enough to trigger the unsuppressed sphaleron processes with baryon number nonconservation. This allows for efficient local electroweak baryogenesis at reheating temperatures T(R)similar toO(10) GeV.

    DOI: 10.1103/PhysRevLett.92.101303

    Web of Science

    researchmap

  • Bulk and brane anomalies in six-dimensions 査読

    Asaka, T., Buchmuller, W., Covi, L.

    Nucl.Phys.B648 ( 1-2 ) 231 - 253   2003年9月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    We study anomalies of six-dimensional gauge theories compactified on orbifolds. In addition to the known bulk anomalies, brane anomalies appear on orbifold fixpoints in the case of chiral boundary conditions. At a fixpoint, where the bulk gauge group G is broken to a subgroup H, the non-Abelian G-anomaly in the bulk reduces to a H-anomaly which depends in a simple manner on the chiral boundary conditions. We illustrate this mechanism by means of a SO(10) GUT model. (C) 2002 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0550-3213(02)00976-8

    Web of Science

    researchmap

  • Quarks and leptons between branes and bulk 査読

    Asaka, T., Buchmuller, W., Covi, L.

    Phys.Lett.B563 ( 3-4 ) 209 - 216   2003年4月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    We study a supersymmetric SO(10) gauge theory in six dimensions compactified on an orbifold. Three sequential quarklepton families are localized at the three fixpoints where SO(10) is broken to its three GUT subgroups. Split bulk multiplets yield the Higgs doublets of the standard model and as additional states lepton doublets and down-quark singlets. The physical quarks and leptons are mixtures of brane and bulk states. The model naturally explains small quark mixings together with large lepton mixings in the charged current. A small hierarchy of neutrino masses is obtained due to the different down-quark and up-quark mass hierarchies. None of the usual GUT relations between fermion masses holds exactly. (C) 2003 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0370-2693(03)00644-0

    Web of Science

    researchmap

  • Lopsided mass matrices and leptogenesis in SO(10) GUT 査読

    Asaka, T.

    Phys.Lett.B562 ( 3-4 ) 291 - 298   2003年4月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    Lopsided structure in mass matrices of down quarks and leptons gives a simple explanation for the observed large angles of neutrino mixings. We realize such mass matrices by the Froggatt-Nielsen mechanism in the framework of supersymmetric SO(10) grand unified theory (GUT). It is shown that the model can reproduce the successful mass matrices which have been obtained in SU(5) models. Cosmological implication of the model is also discussed. We show that the hybrid inflation occurs naturally in the model and it offers non-thermal leptogenesis by decays of the next-to-lightest right-handed neutrinos. The present baryon asymmetry is explained by just the oscillation mass scale in the atmospheric neutrinos. (C) 2003 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0370-2693(03)00611-7

    Web of Science

    researchmap

  • Nonthermal leptogenesis from the heavier Majorana neutrinos 査読

    Asaka, T., Nielsen, H.B., Takanishi, Y.

    Nucl.Phys.B647 ( 1-2 ) 252 - 274   2002年7月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    We investigate a scheme for making leptogenesis by means of the (CP violating decays of the seesaw Majorana neutrinos proposed by Fukugita and Yanagida, However in order to avoid the washout of the produced lepton number we propose the production of the Majorana neutrinos to occur non-thermally and sufficiently late, After this time in consequence, the B - L (baryon minus lepton) quantum number becomes a good "accidental symmetry" protecting the asymmetry produced. This non-thermal leptogenesis at late time is realized by a boson decaying into the Majorana neutrinos with a long lifetime. Suggestively this boson could correspond to a scalar field which causes the cosmic inflation, the inflaton, and thus its decay means really the reheating of the Universe. We find that this mechanism works well even if the lightest Majorana neutrinos are not produced sufficiently or not present, and the decays of the heavier seesaw Majorana neutrino can be responsible to the baryon asymmetry in the present Universe, as we illustrate by the example of the family replicated gauge group model. (C) 2002 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0550-3213(02)00934-3

    Web of Science

    researchmap

  • Exceptional coset spaces and unification in six-dimensions 査読

    Asaka, T., Buchmuller, W., Covi, L.

    Phys.Lett.B540 ( 3-4 ) 295 - 300   2002年4月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    The coset spaces E-8/SO(10) x H-F allow complex structures which can account for three quark-lepton generations including right-handed neutrinos. We show that in the context of supersynametric SO(10) gauge theories in 6 dimensions they also provide the Higgs fields which are needed to break the electroweak and B - L gauge symmetries, and to generate small neutrino masses via the seesaw mechanism. (C) 2002 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0370-2693(02)02153-6

    Web of Science

    researchmap

  • Affleck–Dine leptogenesis and low scale inflation 査読

    T. Asaka

    Physics Letters B521 ( 3-4 ) 329 - 334   2001年10月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/S0370-2693(01)01237-0

    Web of Science

    researchmap

  • Gauge unification in six-dimensions 査読

    Asaka, T., Buchmuller, W., Covi, L.

    Phys.Lett.B523 ( 1-2 ) 199 - 204   2001年8月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    We study the breaking of a supersymmetric SO(10) GUT in 6 dimensions by orbifold compactification. In 4 dimensions we obtain a N = 1 supersymmetric theory with the standard model gauge group enlarged by an additional U(1) symmetry, The 4-dimensional gauge symmetry is obtained as intersection of the Pati-Salam and the Georgi-Glashow subgroups of SO(10). which appear as unbroken subgroups in the two 5-dimensional subspaces, respectively. The doublet-triplet splitting arises as in the recently discussed SU(5) GUTs in 5 dimensions. (C) 2001 Elsevier Science B.V. All fights reserved.

    DOI: 10.1016/S0370-2693(01)01324-7

    Web of Science

    researchmap

  • False vacuum decay after inflation 査読

    Asaka, T., Buchmuller, W., Covi, L.

    Phys.Lett.B510 ( 1-4 ) 271 - 276   2001年4月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    Inflation is terminated by a non-equilibrium process which finally leads to a thermal state. We study the onset of this transition in a class of hybrid inflation models. The exponential growth of tachyonic modes leads to decoherence and spinodal decomposition. We compute the decoherence time, the spinodal time, the size of the formed domains and the homogeneous classical fields within a single domain. (C) 2001 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0370-2693(01)00623-2

    Web of Science

    researchmap

  • Affleck-Dine leptogenesis with an ultralight neutrino 査読

    Asaka, T., Fujii, Masaaki, Hamaguchi, Koichi, Yanagida, T.

    Phys.Rev.D62 ( 12 ) 123514 - 123514   2000年8月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    We perform a detailed analysis on Affleck-Dine leptogenesis taking into account the thermal effects on the dynamics of the flat direction field (Formula presented) We find that an extremely small mass for the lightest neutrino (Formula presented) is required to produce enough lepton-number asymmetry to explain the baryon asymmetry in the present Universe. We impose here the reheating temperature after inflation (Formula presented) to be (Formula presented) to solve the cosmological gravitino problem. The required value of the neutrino mass seems to be very unlike the case since the recent SuperKamiokande experiments suggest the masses of the heavier two neutrinos (Formula presented) and (Formula presented) to be in a range of (Formula presented) We also propose a model to avoid this difficulty based on the Peccei-Quinn symmetry, where the required neutrino mass can be as large as (Formula presented). © 2000 The American Physical Society.

    DOI: 10.1103/PhysRevD.62.123514

    Scopus

    researchmap

  • Leptogenesis in inflationary universe 査読

    Asaka, T., Hamaguchi, Koichi, Kawasaki, M., Yanagida, T.

    Phys.Rev.D61 ( 8 ) 083512 - 083512   2000年7月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    We investigate leptogenesis via decays of heavy Majorana neutrinos which are produced nonthermally in inflaton decays. We make a comprehensive study on leptogenesis assuming various supersymmetric (SUSY) models for hybrid, new, and topological inflations. For an estimation of the lepton asymmetry we adopt the Froggatt-Nielsen mechanism for mass matrices of quarks and leptons. We find that all of these models are successful in producing enough lepton asymmetry to explain the baryon number in the present universe. Here we impose low reheating temperatures such as (Formula presented) in order to suppress the abundance of gravitinos so they do not conflict with big-bang nucleosynthesis. Furthermore, we find that leptogenesis works very well even with (Formula presented) in the SUSY hybrid or new inflation model. It is known that such a reheating temperature is low enough to suppress the abundance of gravitinos of mass (Formula presented)–1 TeV. Thus, leptogenesis is fully consistent with big-bang nucleosynthesis in a wide region of the gravitino mass. © 2000 The American Physical Society.

    DOI: 10.1103/PhysRevD.61.083512

    Scopus

    researchmap

  • Solving the gravitino problem by axino 査読

    Asaka, T., Yanagida, T.

    Phys.Lett.B494 ( 3-4 ) 297 - 301   2000年6月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    In a large class of supersymmetric (SUSY) axion models the mass of the axino a (a fermionic superpartner of the axion) is predicted as m((a) over tilde) less than or similar to O(1) keV. Thus, the axino is the lightest SUSY particle (LSP). We pointed out that such a light axino provides a natural solution to the gravitino problem, if the gravitino is the next LSP. We derive a constraint on the reheating temperature T-R of inflation, T-R less than or similar to 10(15) GeV for the gravitino mass m(3/2) similar or equal to 100 GeV, which is much weaker than that obtained in the minimal SUSY standard model. (C) 2000 Published by Elsevier Science B.V.

    DOI: 10.1016/S0370-2693(00)01209-0

    Web of Science

    researchmap

  • Initial condition for new inflation in supergravity 査読

    Asaka, T., Kawasaki, M., Yamaguchi, Masahide

    Phys.Rev.D61   027303 - 027303   2000年6月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1103/PhysRevD.61.027303

    researchmap

  • Cosmological gravitino problem in gauge mediated supersymmetry breaking models 査読

    Asaka, T., Hamaguchi, Koichi, Suzuki, Koshiro

    Phys.Lett.B490 ( 1-2 ) 136 - 146   2000年5月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    We investigate the cosmological gravitino problem in gauge-mediated supersymmerry breaking models, where the gravitino becomes in general the lightest supersymmetric particle (LSP). In order to avoid the overclosure of the stable gravitino, the reheating temperature of inflation T-R should be low enough. Furthermore, if the gravitino moss is larger than about 100 MeV, the decay of the next-to-LSP (NLSP) into the gravitino may modify disastrously the abundances of the light elements predicted by the big-bang nucleosynthesis (BBN). We consider the case in which the lighter stau is the NLSP and derive cosmological constraints from the BBN on the stau NLSP decay. We obtain a lower bound on the mass of stau m(tau)over-bar-1, which is more stringent than the current experimental limit m(tau)over-bar-1 > 90 GeV for the gravitino mass region m(3/2) greater than or similar to 5 GeV. This lower bound, together with the overclosure constraint on the stable gravitino, gives an upper bound on T-R. We find that the reheating temperature can be as high as 10(9)-10(10) GeV for m(3/2) similar or equal to 5-100 GeV. (C) 2000 Published by Elsevier Science B.V.

    DOI: 10.1016/S0370-2693(00)00959-X

    Web of Science

    researchmap

  • Hadronic axion model in gauge mediated supersymmetry breaking and cosmology of saxion 査読

    Asaka, T., Yamaguchi, Masahiro

    Phys.Rev.D59 ( 12 ) 125003 - 125003   1999年11月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    Recently we proposed a simple hadronic axion model within gauge-mediated supersymmetry breaking. In this paper we discuss various cosmological consequences of the model in great detail. Particular attention is paid to the saxion, a scalar partner of the axion, which is produced as a coherent oscillation in the early universe. We show that our model is cosmologically viable if the reheating temperature of inflation is sufficiently low. We also discuss the late decay of the saxion which gives a preferable power spectrum of the density fluctuation in the standard cold dark matter model when compared with observations. © 1999 The American Physical Society.

    DOI: 10.1103/PhysRevD.59.125003

    Scopus

    researchmap

  • Cosmological moduli problem and oscillating inflation in gauge mediated supersymmetry breaking 査読

    Asaka, T., Kawasaki, M., Yamaguchi, Masahide

    Phys.Lett.B451 ( 3-4 ) 317 - 323   1999年10月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier  

    We investigate cosmological moduli problem in the gauge-mediated supersymmetry breaking (GMSB). A mini-inflation (oscillating inflation) takes place when a scalar field corresponding to the flat direction in GMSB oscillates along the logarithmic potential induced by the gauge-mediation mechanism. It is shown that this oscillating inflation can sufficiently dilute the relic abundance of the string moduli for some ranges of parameters in the GMSB models. © 1999 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0370-2693(99)00213-0

    Scopus

    researchmap

  • Leptogenesis in inflaton decay 査読

    Asaka, T., Hamaguchi, Koichi, Kawasaki, M., Yanagida, T.

    Phys.Lett.B464 ( 1-2 ) 12 - 18   1999年6月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    We study a leptogenesis via decays of heavy Majorana neutrinos produced non-thermally in inflation decays. We find that this scenario is fully consistent with existing supersymmetric inflation models such as for topological or for hybrid inflation and the Froggatt-Nielsen mechanism generating hierarchies in quark and lepton mass matrices. The reheating temperature T-R of inflation may be taken as low as T-R similar or equal to 10(8) GeV to avoid the cosmological gravitino problem. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0370-2693(99)01020-5

    Web of Science

    researchmap

  • Cosmological moduli problem and thermal inflation models 査読

    Asaka, T., Kawasaki, M.

    Phys.Rev.D60 ( 12 ) 123509 - 123509   1999年5月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    In superstring theories, there exist various dilaton and modulus fields whose masses are expected to be of the order of the gravitino mass (Formula presented) These fields lead to serious cosmological difficulties, the so called “cosmological moduli problem,” because a large number of moduli particles are produced as the coherent oscillations after primordial inflation. We make a comprehensive study of whether the thermal inflation can solve the cosmological moduli problem in the whole modulus mass region (Formula presented) predicted by both hidden sector supersymmetry (SUSY) breaking and gauge-mediated SUSY breaking models. In particular, we take into account the primordial inflation model whose reheating temperature is so low that its reheating process finishes after the thermal inflation ends. We find that the above mass region (Formula presented) survives from various cosmological constraints in the presence of thermal inflation. © 1999 The American Physical Society.

    DOI: 10.1103/PhysRevD.60.123509

    Scopus

    researchmap

  • Superheavy dark matter and thermal inflation 査読

    Asaka, T., Kawasaki, M., Yanagida, T.

    Phys.Rev.D60 ( 10 ) 103518 - 103518   1999年4月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    Thermal inflation is the most plausible mechanism that solves the cosmological moduli problem naturally. We discuss the relic abundance of a superheavy particle X in the presence of thermal inflation, assuming that its lifetime is longer than the age of the universe, and show that the long-lived particle X of mass (Formula presented) GeV may form a part of the dark matter in the present universe in a wide region of parameter space of the thermal inflation model. The superheavy dark matter of mass (Formula presented) GeV may be interesting in particular, since its decay may account for the observed ultrahigh-energy cosmic rays if the lifetime of the X particle is sufficiently long. © 1999 The American Physical Society.

    DOI: 10.1103/PhysRevD.60.103518

    Scopus

    researchmap

  • Cosmological moduli problem in gauge mediated supersymmetry breaking theories 査読

    Asaka, T., Hashiba, J., Kawasaki, M., Yanagida, T.

    Phys.Rev.D58 ( 8 ) 083509 - 083509   1998年11月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    A generic class of string theories predicts the existence of light moduli fields, and they are expected to have masses (Formula presented) comparable to the gravitino mass (Formula presented) which is in a range of (Formula presented) keV to 1 GeV in gauge-mediated supersymmetry breaking theories. Such light fields with weak interactions suppressed by the Planck scale cannot avoid some stringent cosmological constraints
    that is, they suffer from “cosmological moduli problems.” We show that the total gravitino mass region (Formula presented) keV(Formula presented) GeV is excluded by the constraints even if we incorporate late-time mini-inflation (thermal inflation). However, a modification of the original thermal inflation model enables the region (Formula presented) keV(Formula presented) keV to survive the constraints. It is also stressed that the moduli can be dark matter in our universe for the mass region (Formula presented) keV(Formula presented) keV. © 1998 The American Physical Society.

    DOI: 10.1103/PhysRevD.58.083509

    Scopus

    researchmap

  • Hadronic axion model in gauge mediated supersymmetry breaking 査読

    Asaka, T., Yamaguchi, Masahiro

    Phys.Lett.B437 ( 1-2 ) 51 - 61   1998年5月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    A simple hadronic axion model is proposed in the framework of gauge-mediated supersymmetry breaking. Dynamics of Peccei-Quinn symmetry breaking is governed by supersymmetry breaking effects and the Peccei-Quinn breaking scale f(PQ) is inversely proportional to the gravitino mass. The gravitino mass range which corresponds to the axion window f(PQ) similar or equal to 10(9) GeV - 10(13) GeV lies in the region predicted by gauge-mediated supersymmetry breaking models. The model is also shown to be cosmologically viable. (C) 1998 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0370-2693(98)00890-9

    Web of Science

    researchmap

  • Spectrum of background x-rays from moduli dark matter 査読

    Asaka, T., Hashiba, J., Kawasaki, M., Yanagida, T.

    Phys.Rev.D58 ( 2 ) 023507 - 023507   1998年2月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    We examine the x-ray spectrum from the decay of dark-matter moduli with mass (Formula presented) in particular, paying attention to the line spectrum from the moduli trapped in the halo of our galaxy. It is found that with the energy resolution of the current experiments (Formula presented) the line intensity is about twice as strong as that of the continuum spectrum from the moduli that spread in the whole universe. Therefore, in future experiments with higher energy resolutions it may be possible to detect such line photons. We also investigate the γ-ray spectrum emitted from the decay of the multi-GeV moduli. It is shown that the emitted photons may form a MeV bump in the γ-ray spectrum. We also find that if the modulus mass is of the order of 10 GeV, the emitted photons at the peak of the continuum spectrum lose their energy by scattering and the shape of the spectrum is significantly changed, which makes the constraint weaker than that obtained in previous works. © 1998 The American Physical Society.

    DOI: 10.1103/PhysRevD.58.023507

    Scopus

    researchmap

  • Probing Dynamical Symmetry Breaking Using Top Quark

    T. Asaka, N. Maekawa, T. Moroi, Y. Shobuda, Y. Sumino

    Progress of Theoretical Physics, Supplement123   151 - 161   1996年12月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)  

    Proceedings of YKIS '95

    researchmap

  • Top mass and isospin breaking in dynamical symmetry breaking scenario 査読

    Asaka, T., Shobuda, Y., Sumino, Y.

    Phys.Rev.D54 ( 9 ) 5698 - 5704   1996年5月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER PHYSICAL SOC  

    We consider a scenario where the top-quark mass is generated dynamically, and study the implications of the present experimental values for m(t) and the T parameter. We assume a technicolorlike scenario for inducing the W mass and an effective four-Fermi operator for inducing the top-quark mass. We also assume that only this four-Fermi operator is relevant at low energy. Then we estimate in detail the strength G and the intrinsic mass scale M of the four-Fermi operator. A unitarity bound is used to quantify the strength of G, We find that G/4 pi similar to 1 and that M is of the order of Lambda(TC)similar or equal to 1-2 TeV or less. Namely the four-Fermi operator cannot be treated as ''pointlike'' around the electroweak scale. Furthermore we estimate the contribution of the four-Fermi operator to the T parameter. We find that the QCD correction to the top-quark mass function reduces the contribution to the T parameter by about 40%. By comparing the results with the present experimental bound, we obtain another upper bound on M which is typically in the several to 10 TeV region.

    DOI: 10.1103/PhysRevD.54.5698

    Web of Science

    researchmap

  • Four fermion decay of Higgs bosons 査読

    Asaka, T., Hikasa, Ken-ichi

    Phys.Lett.B345 ( 1 ) 36 - 41   1995年11月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    We calculate four-fermion decays of a Higgs boson via WW and/or ZZ intermediate states for Higgs masses below m(w). We examine models with a doubly-charged Higgs boson H++ and show that the four-fermion decay is the dominant mode for a wide range of parameter space. Existing searches for H++ in Z decays have not looked for this mode. We also derive four-fermion decay rate for a neutral Higgs boson.

    DOI: 10.1016/0370-2693(94)01599-8

    Web of Science

    researchmap

▶ 全件表示

MISC

  • Precision electroweak shift of muonium hyperfine splitting

    T. Asaka, M. Tanaka, K. Tsumura, M. Yoshimura

        2018年10月

     詳細を見る

    Electroweak second order shifts of muonium ($\mu^+e^-$ bound state) energy
    levels are calculated for the first time. Calculation starts from on-shell
    one-loop elastic $\mu^+ e^-$ scattering amplitudes in the center of mass frame,
    proceed to renormalization and to derivation of muonium matrix elements by
    using the momentum space wave functions. This is a reliable method unlike the
    unjustified four-Fermi approximation in the literature. Corrections of order
    $\alpha G_F$ (with $\alpha \sim 1/137$ the fine structure constant and $G_F$
    the Fermi constant) and of order $\alpha G_F /(m_Z a_B)$ (with $m_Z$ the Z
    boson mass and $a_B$ the Bohr radius) are derived from three classes of Feynman
    diagrams, Z self-energy, vertex and box diagrams. The ground state muonium
    hyperfine splitting is given in terms of the only experimentally unknown
    parameter, the smallest neutrino mass. It is however found that the neutrino
    mass dependence is very weak, making its detection difficult.

    researchmap

    その他リンク: http://arxiv.org/pdf/1810.05429v1

  • Probing Baryon Asymmetry of the Universe by Using Lepton Universality

    Takehiko Asaka, Shintaro Eijima, Kazuhiro Takeda

        2015年6月

     詳細を見る

    掲載種別:機関テクニカルレポート,技術報告書,プレプリント等  

    We study the model with three right-handed neutrinos which masses are smaller<br />
    than the weak scale ${\cal O}(10^2)$ GeV (called as the $\nu$MSM). The model<br />
    can explain the origin of neutrino masses by the seesaw mechanism, offer a<br />
    candidate of dark matter and realize the baryogenesis via neutrino oscillation.<br />
    The seesaw mechanism at such energy scales can induce phenomenon which are<br />
    observable by experiments. As an example, we discuss the lepton universality of<br />
    charged kaon decays in this model. It is shown that the heavy neutral leptons<br />
    accounting for the neutrino masses and the cosmic baryon asymmetry can give a<br />
    significant correction to the lepton universality, and that the deviation from<br />
    the Standard Model prediction can be large as ${\cal O}(10^{-3})$ which will be<br />
    probed by near future experiments.

    researchmap

  • Masses and Mixing of Quarks and Leptons in Product-Group Unification

    Takehiko Asaka, Y. Takanishi

        2004年9月

     詳細を見る

    掲載種別:機関テクニカルレポート,技術報告書,プレプリント等  

    We discuss a supersymmetric unified model based on a product gauge group<br />
    SU(5)\times SU(5)\times SU(5), where the gauge symmetry breaking is achieved<br />
    without the adjoint or higher-dimensional Higgs field, and the doublet-triplet<br />
    splitting in the Higgs masses is realized by the use of the discrete symmetry.<br />
    In this article we present an explicit model for realistic fermion masses with<br />
    the discrete symmetries Z_7\times Z_2. It is shown that all the observed masses<br />
    and mixing angles for quarks and leptons, including neutrinos, are well<br />
    described by the breaking of the symmetries imposed in the model. Especially,<br />
    the maximal and large mixing angles in the atmospheric and solar neutrino<br />
    oscillations are obtained as the most preferred values, and the typical value<br />
    of the neutrino mixing element U_{e3} is 0.1-0.3. We also point out the<br />
    non-trivial relations among the \mu-parameter for the Higgs mass, the charged<br />
    fermion hierarchies, and the neutrino masses. These relations suggest that the<br />
    scale of \mu is of order of the weak scale.

    researchmap

共同研究・競争的資金等の研究

  • 暗黒物質から探る標準模型を超えた新物理

    研究課題/領域番号:20H01898  2020年04月 - 2024年03月

    日本学術振興会  科学研究費助成事業 基盤研究(B)  基盤研究(B)

    淺賀 岳彦

      詳細を見る

    配分額:17160000円 ( 直接経費:13200000円 、 間接経費:3960000円 )

    researchmap

  • 原始重力波を用いたニュートリノ質量獲得機構の解明

    研究課題/領域番号:19H05097  2019年04月 - 2021年03月

    日本学術振興会  科学研究費助成事業 新学術領域研究(研究領域提案型)  新学術領域研究(研究領域提案型)

    淺賀 岳彦

      詳細を見る

    配分額:2340000円 ( 直接経費:1800000円 、 間接経費:540000円 )

    researchmap

  • 質量階層性に対する新しい原理が導く多彩な物理現象とプランクスケールの物理

    研究課題/領域番号:18H03708  2018年04月 - 2023年03月

    日本学術振興会  科学研究費助成事業 基盤研究(A)  基盤研究(A)

    磯 暁, 淺賀 岳彦, 川合 光

      詳細を見る

    配分額:43290000円 ( 直接経費:33300000円 、 間接経費:9990000円 )

    researchmap

  • 地上実験による宇宙暗黒物質と宇宙バリオン数の起源解明

    研究課題/領域番号:17K05410  2017年04月 - 2020年03月

    日本学術振興会  科学研究費助成事業 基盤研究(C)  基盤研究(C)

    淺賀 岳彦

      詳細を見る

    配分額:3510000円 ( 直接経費:2700000円 、 間接経費:810000円 )

    本課題では、標準模型における宇宙暗黒物質、および宇宙バリオン数の起源の問題を解決し、ニュートリ ノ質量の起源も同時に解決する理論の探求を進めている。その際、振動実験では不明のニュートリノ質量の絶対値、さらにはニュートリノがディラック粒子かマヨラナ粒子かなど、ニュートリノの基本的性質を把握する事が重要である。
    本年度の研究実績の一つとして、ニュートリノの性質を解明するために、正の電荷を持ったミューオンと電子の束縛状態(ミューオニウム)を考え、その超微細構造に対するニュートリノ対の寄与を評価した。先行研究ではこの寄与をフェルミの4体相互作用を用いて評価してきた。我々は、世界で初めて、標準模型に基づき電弱相互作用の2次の補正として計算を実行した。その結果、これまではフェルミ定数の二乗の寄与とされてきたが、実際にはニュートリノ対に寄与はフェルミ定数と微細構造定数の積に比例する事が判明した。また定量的には、ニュートリノ対の寄与は非常に小さいこと、さらにニュートリノ質量に対する依存性は無視できるほど小さい事が示せた。この結果、電弱相互作用の二次の補正は現在の観測精度と比べると小さいため、実験的に標準模型からズレが今後観測された場合、それは新物理の寄与を示す事がわかった。この論文は、arXivに発表すると共に、現在査読付雑誌に投稿中である。
    ”Precision electroweak shift of muonium hyperfine splitting”, by T. Asaka, M. Tanaka, K. Tsumura, M.Yoshimura, [arXiv:1810.05429].

    researchmap

  • 電弱スケールでの共鳴レプトン数生成機構

    研究課題/領域番号:17H05198  2017年04月 - 2019年03月

    日本学術振興会  科学研究費助成事業 新学術領域研究(研究領域提案型)  新学術領域研究(研究領域提案型)

    淺賀 岳彦

      詳細を見る

    配分額:1950000円 ( 直接経費:1500000円 、 間接経費:450000円 )

    標準模型では説明できないニュートリノ質量と宇宙バリオン数非対称性の問題に対する解決策として右巻きニュートリノを導入した拡張模型を検討した。本研究では、TeVスケールの質量を持つ右巻きニュートリノの物理を詳細に検討した。この場合、質量が縮退した右巻きニュートリノを導入することにより共鳴レプトン数生成機構が働くことが知られている。我々はボルツマン方程式を用いた数値解析を用いて、共鳴レプトン数生成機構による宇宙バリオン数非対称性を評価した。特に、鍵となるCP対称性の破れが、地上実験で検証可能な左巻きニュートリノセクターで引き起こされる場合を検討した。
    第一の成果として、宇宙バリオン数非対称性の正しい符号を与えるCP対称性の破れのパターンを示した。特に、正しい符号を与えるDirac CP位相とMajorana CP位相の範囲をニュートリノ質量階層性ごとに示した。
    第二の成果として、宇宙バリオン数非対称性の生成量とニュートリノを伴わない二重ベータ崩壊における有効ニュートリノ質量の間の相関関係を示した。特に、宇宙バリオン数非対称性の観測量を説明するためには、有効ニュートリノ質量に制限が付くことを示した。右巻きニュートリノの質量差が大きくなると有効質量に厳しい上限が得られることを指摘した。
    本成果については、論文としてまとめarXivへ発表すると共に、査読付き雑誌へ投稿中である。
    "Resonant leptogenesis at TeV-scale and neutrinoless double beta decay",
    by Takehiko Asaka and Takahiro Yoshida, [arXiv:1812.11323].

    researchmap

  • レプトン数の破れから探る宇宙バリオン数生成機構の解明

    研究課題/領域番号:15H01031  2015年04月 - 2017年03月

    日本学術振興会  科学研究費助成事業 新学術領域研究(研究領域提案型)  新学術領域研究(研究領域提案型)

    淺賀 岳彦

      詳細を見る

    配分額:1950000円 ( 直接経費:1500000円 、 間接経費:450000円 )

    宇宙における物質の数と反物質の数との差、つまり宇宙バリオン数の起源の解明を目指し、新しい素粒子理論の枠組みを検討した。特に、素粒子標準模型に、電弱スケール以下の質量をもつ「軽い右巻きニュートリノ」を新たに導入した拡張理論を考察した。この模型の特徴は、宇宙バリオン数の起源だけでなく、ニュートリノ質量起源も同時に説明できる点である。さらに、新粒子の質量が軽いために、実験検証が可能という特徴も持つ。本課題ではこの「軽い右巻きニュートリノ」が引き起こすレプトン数を破る現象を研究した。
    <BR>
    今年度の研究成果の一つとして、「軽い右巻きニュートリノ」が引き起こすニュートリノを伴わない二重ベータ崩壊が上げられる。この崩壊過程はレプトン数をふたつ破る過程であり、標準模型では禁止される。そのため、新物理発見のための重要な反応である。我々は、この過程に対する「軽い右巻きニュートリノ」の寄与を定量的に評価し、その質量が500MeV程度の場合には通常のマヨラナニュートリノに対し付加的な寄与を与え、崩壊を加速させることを示した。この成果は、今後のKamLAND-Zen実験等での観測可能性が高くなることを示しており、幅広い分野に重要なインパクトを与えた。
    <BR>
    また、B中間子のレプトン数を破る崩壊過程についても研究成果がある。この過程は、中間状態に「軽い右巻きニュートリノ」が媒介することにより生じる。我々は、この過程の反応率を定量的に評価し、今後のBelle-II実験、およびFuture Circular Collider(FCC)計画での測定感度を求めた。その結果、これらの実験計画で検証可能性がある事を指摘した。特に、FCC計画では右巻きニュートリノの混合角の大きさとして千分の一程度まで検証可能であることを示した。

    researchmap

  • 軽い右巻きニュートリノの宇宙物理と実験検証

    研究課題/領域番号:26105508  2014年04月 - 2016年03月

    日本学術振興会  科学研究費助成事業 新学術領域研究(研究領域提案型)  新学術領域研究(研究領域提案型)

    淺賀 岳彦

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

    配分額:3510000円 ( 直接経費:2700000円 、 間接経費:810000円 )

    素粒子標準模型の抱えるニュートリノ質量、宇宙暗黒物質、および宇宙バリオン数の問題を同時に解決する可能性として、新しい素粒子、「電弱スケールよりも軽い右巻きニュートリノ」に着目した。特に、この粒子の実験による検証可能性について検討を行った。
    <BR>
    今年度は科研費のサポートを受け研究が進展し、合計6編の論文を発表した。内訳は、査読付き論文に発表済みが3編、論文に投稿中が2編、会議紀要が1編が1編である。また研究成果は、国内外の研究会で多数発表してきた。特に、国際会議2回を含む計4回、招待講演を行った。
    <BR>
    注目すべき研究成果としては、J-Parc加速器にて計画されているCOMET実験において軽い右巻きニュートリノを探索する手法を提案した。COMET実験は、大強度ミューオンを用いてレプトンフレーバーを変えるミューオン電子転換過程を探索する実験である。本研究では、この実験装置をそのまま用い、質量が1MeVから100MeVの右巻きニュートリノを探索する方法を提示した。この領域であるとCOMET実験において大量に生成するミュー粒子の崩壊から右巻きニュートリノが生成可能である。さらに、1MeVよりも重いと右巻きニュートリノはニュートリノと電子対へ崩壊する。この電子対の発生をシグナルとした。我々の解析から、COMET実験での右巻きニュートリノの感度は、CERNでのPS191実験が制限した領域と同程度であり、これまで未探索の領域まで達することが判明した。

    researchmap

  • 宇宙物質創成機構の解明と新しい素粒子理論の構築

    研究課題/領域番号:25400249  2013年04月 - 2017年03月

    日本学術振興会  科学研究費助成事業 基盤研究(C)  基盤研究(C)

    淺賀 岳彦, 渡邊 篤史, 谷本 盛光, 中野 博章

      詳細を見る

    担当区分:研究代表者  資金種別:競争的資金

    配分額:4810000円 ( 直接経費:3700000円 、 間接経費:1110000円 )

    振動実験から明らかになったニュートリノ質量の起源を手がかりに新しい素粒子の理論的枠組みを探求した。特に、ニュートリノ質量、宇宙暗黒物質、および宇宙バリオン数を同時に説明する可能性を持つ右巻きニュートリノの物理を検討した。本研究では、質量が電弱スケール(100GeV程度)よりも軽い場合を考え、宇宙バリオン数を生成する機構、および右巻きニュートリノを地上実験での探索可能性について研究を行った。

    researchmap

  • ステライルニュートリノの質量・混合の生成機構とその現象論的解明

    研究課題/領域番号:24654062  2012年04月 - 2015年03月

    日本学術振興会  科学研究費助成事業 挑戦的萌芽研究  挑戦的萌芽研究

    谷本 盛光, 淺賀 岳彦

      詳細を見る

    配分額:2600000円 ( 直接経費:2000000円 、 間接経費:600000円 )

    本研究では、ステライルニュートリノの質量と混合に焦点をあて、ニュートリノモデルの現象論的研究に成果をあげた。まず、ステライルニュートリノが存在する条件下で、通常のアクティブニュートリノの質量と大きなニュートリノ混合角を最小限のパラメータで説明できるモデルを構築した。そこでは混合角θ12 が精密に予言できるため、将来ニュートリノ実験でテスト可能である。さらに、ニュートリノのCP対称性の破れはフレーバー対称性の破れで予言できることを発見した。その成果は、1編の著書と20編の論文として発表するとともに、著名な国際会議ニュートリノ2014(2014年6月:ボストン)において招待講演として発表した。

    researchmap

  • 離散世代対称性をもつ超共形ダイナミクスに基づく素粒子模型

    研究課題/領域番号:22540269  2010年 - 2012年

    日本学術振興会  科学研究費助成事業 基盤研究(C)  基盤研究(C)

    中野 博章, 谷本 盛光, 淺賀 岳彦, 吉岡 興一

      詳細を見る

    配分額:2860000円 ( 直接経費:2200000円 、 間接経費:660000円 )

    超対称性は,電弱対称性の破れの起源を探る上で魅力的なアイデアである。本研究では,フレーバー非保存過程の抑制機構と暗黒物質の関係に着目した。フレーバー非保存を抑制機構としては,超共形相互作用によるものと連続的R対称性によるものの二つの場合を検討した。特に後者において,R対称性の破れを表すグラビティーノ質量と,ニュートリノ質量の生成機構および陽子安定性の関係を得た。

    researchmap

  • 素粒子の世代対称性とその検証

    研究課題/領域番号:21340055  2009年04月 - 2014年03月

    日本学術振興会  科学研究費助成事業 基盤研究(B)  基盤研究(B)

    谷本 盛光, 中野 博章, 淺賀 岳彦

      詳細を見る

    配分額:18720000円 ( 直接経費:14400000円 、 間接経費:4320000円 )

    本計画の主たる目的は、素粒子の世代に非可換離散対称を課し、その現象論的研究を行うものである。ニュートリノの世代混合角をフレーバー対称性で理解することをベースにして、その対称性によってクォークとレプトンの世代構造にとどまらず、超対称性粒子、すなわちスクォークとスレプトンの世代構造に制限を与えることである。
    ① ニュートリノ振動実験で測定されたフレーバー混合角θ13の大きさは非可換離散対称性A4またはS4によって説明できることを示した。
    ②LHCbにおけるB中間子のCP対称性の破れの分析からスクォークの世代混合の構造に強い制限を与えることに成功した。

    researchmap

  • 宇宙の進化を記述する素粒子統一模型の構築

    研究課題/領域番号:21540260  2009年 - 2012年

    日本学術振興会  科学研究費助成事業 基盤研究(C)  基盤研究(C)

    淺賀 岳彦, 谷本 盛光, 中野 博章

      詳細を見る

    資金種別:競争的資金

    配分額:4290000円 ( 直接経費:3300000円 、 間接経費:990000円 )

    ニュートリノ質量、宇宙暗黒物質、および宇宙バリオン数の起源を手がかりに、標準模型を超えた新しい素粒子理論の構築について研究した。特に、質量が電弱スケールより軽い右巻きニュートリノに着目し、この新素粒子の引き起こす様々な物理現象を検討した。本研究では、右巻きニュートリノの世代間混合に起因した宇宙バリオン数生成量の新しい評価法を開発すると共に、地球大気や地上加速器で生成された右巻きニュートリノの観測可能性を議論した。

    researchmap

  • ニュートリノで探る現在の宇宙像

    研究課題/領域番号:18740122  2006年 - 2007年

    日本学術振興会  科学研究費助成事業 若手研究(B)  若手研究(B)

    浅賀 岳彦

      詳細を見る

    資金種別:競争的資金

    配分額:2200000円 ( 直接経費:2200000円 )

    新しい素粒子右巻きニュートリノの導入により、宇宙物理の謎を解明する。

    researchmap

  • 超対称性に基づく素粒子の統一理論と宇宙物理

    研究課題/領域番号:99J08791  1999年 - 2000年

    日本学術振興会  科学研究費助成事業 特別研究員奨励費  特別研究員奨励費

    浅賀 岳彦

      詳細を見る

    配分額:2400000円 ( 直接経費:2400000円 )

    researchmap

▶ 全件表示

 

担当経験のある授業科目

  • 量子力学IIB

    2020年
    -
    現在
    機関名:新潟大学

  • 現代物理学セミナーB

    2020年
    -
    現在
    機関名:新潟大学

  • 量子力学IIA

    2020年
    -
    現在
    機関名:新潟大学

  • 現代物理学セミナーA

    2020年
    -
    現在
    機関名:新潟大学

  • 物理学特論II

    2020年
    -
    現在
    機関名:新潟大学

  • 素粒子物理学

    2019年
    -
    現在
    機関名:新潟大学

  • 理学スタディ・スキルズ

    2018年
    -
    2019年
    機関名:新潟大学

  • 素粒子物理学I

    2017年
    機関名:新潟大学

  • 論文演習

    2015年
    機関名:新潟大学

  • 数理物質科学特定研究Ⅲ(物理学)

    2015年
    機関名:新潟大学

  • 研究発表演習・発表Ⅲ

    2015年
    機関名:新潟大学

  • 数理物質科学演習Ⅲ(物理学)

    2015年
    機関名:新潟大学

  • 理論素粒子物理学III

    2014年
    -
    現在
    機関名:新潟大学

  • 量子力学II

    2014年
    -
    現在
    機関名:新潟大学

  • 研究発表演習・発表Ⅰ

    2014年
    -
    2015年
    機関名:新潟大学

  • 研究発表演習・発表Ⅱ

    2014年
    -
    2015年
    機関名:新潟大学

  • 数理物質科学特定研究Ⅱ(物理学)

    2014年
    -
    2015年
    機関名:新潟大学

  • 素粒子物理学II

    2013年
    -
    2018年
    機関名:新潟大学

  • 数理物質科学特定研究ⅡA(物理学)

    2013年
    -
    2015年
    機関名:新潟大学

  • 数理物質科学特定研究ⅡB(物理学)

    2013年
    -
    2015年
    機関名:新潟大学

  • 数理物質科学演習Ⅱ(物理学)

    2013年
    -
    2015年
    機関名:新潟大学

  • 数理物質科学演習Ⅰ(物理学)

    2013年
    -
    2015年
    機関名:新潟大学

  • 数理物質科学特定研究Ⅰ(物理学)

    2013年
    -
    2015年
    機関名:新潟大学

  • 現代物理学への招待(物理学学習法)

    2013年
    機関名:新潟大学

  • 物理学基礎A I

    2011年
    -
    現在
    機関名:新潟大学

  • 課題探索特講

    2010年
    -
    2014年
    機関名:新潟大学

  • 物理学演習

    2010年
    機関名:新潟大学

  • ゲージ場理論特論Ⅲ

    2008年
    -
    現在
    機関名:新潟大学

  • 物理数学I

    2008年
    -
    2013年
    機関名:新潟大学

  • 対称性とゲージ場理論

    2008年
    -
    2013年
    機関名:新潟大学

  • 量子力学演習II

    2007年
    -
    現在
    機関名:新潟大学

  • 物理数学演習II

    2007年
    -
    2009年
    機関名:新潟大学

▶ 全件表示