Updated on 2024/04/20

写真a

 
ASAKA Takehiko
 
Organization
Academic Assembly Institute of Science and Technology Fundamental Sciences Professor
Faculty of Science Department of Science Professor
Title
Professor
External link

The Best Research Achievement in Research Career

Degree

  • Doctor (Science) ( 1997.3   Tohoku University )

Research Interests

  • Theoretical Particle Physics

Research Areas

  • Natural Science / Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics

Research History (researchmap)

  • Niigata University   Graduate School of Science and Technology Fundamental Sciences   Professor

    2019.4

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  • Niigata University   Faculty of Science Department of Science   Professor

    2019.4

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  • Niigata University   Faculty of Science Department of Science   Associate Professor

    2017.4 - 2019.3

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  • Niigata University   Graduate School of Science and Technology Fundamental Sciences   Associate Professor

    2010.4 - 2019.3

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  • Niigata University   Faculty of Science Department of Physics Fundamental Physics   Associate Professor

    2007.9 - 2017.3

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  • École polytechnique fédérale de Lausanne (EPFL)   Researcher

    2006.10 - 2007.9

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  • Graduate School of Science, Tohoku University   Researcher

    2005.9 - 2006.9

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  • École polytechnique fédérale de Lausanne (EPFL)   Researcher

    2003.10 - 2005.8

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  • University of Lausanne   Researcher

    2002.9 - 2003.9

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  • Deutsches Elektronen-Synchrotron (DESY), Theory Group   Researcher

    2000.9 - 2002.8

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  • Graduate School of Science, University of Tokyo   Special researcher of the Japan Society for the Promotion of Science

    1999.4 - 2000.8

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  • Institute for Cosmic Ray Research, University of Tokyo   Researcher

    1997.4 - 1999.3

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Research History

  • Niigata University   Faculty of Science Department of Science   Professor

    2019.4

  • Niigata University   Faculty of Science Department of Science   Associate Professor

    2017.4 - 2019.3

  • Niigata University   Graduate School of Science and Technology Fundamental Sciences   Associate Professor

    2010.4 - 2019.3

  • Niigata University   Graduate School of Science and Technology Fundamental Sciences   Associate Professor

    2010.4 - 2019.3

  • Niigata University   Abolition organization Fundamental Physics   Associate Professor

    2007.9 - 2017.3

Education

  • Tohoku University   Graduate School, Division of Natural Science   Department of Physics

    - 1997.3

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    Country: Japan

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Papers

  • Neutrinoless double beta decays tell nature of right-handed neutrinos Reviewed

    Takehiko Asaka, Hiroyuki Ishida, Kazuki Tanaka

    Journal of High Energy Physics   2023 ( 7 )   2023.7

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    Publishing type:Research paper (scientific journal)   Publisher:Springer Science and Business Media LLC  

    Abstract

    We consider the minimal seesaw model, the Standard Model extended by two right-handed neutrinos, for explaining the neutrino masses and mixing angles measured in oscillation experiments. When one of right-handed neutrinos is lighter than the electroweak scale, it can give a sizable contribution to neutrinoless double beta (0νββ) decay. We show that the detection of the 0νββ decay by future experiments gives a significant implication to the search for such a light right-handed neutrino.

    DOI: 10.1007/jhep07(2023)062

    arXiv

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    Other Link: https://link.springer.com/article/10.1007/JHEP07(2023)062/fulltext.html

  • What if a specific neutrinoless double beta decay is absent? Reviewed

    Takehiko Asaka, Hiroyuki Ishida, Kazuki Tanaka

    Progress of Theoretical and Experimental Physics   2021 ( 6 )   2021.6

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    Publishing type:Research paper (scientific journal)   Publisher:Oxford University Press (OUP)  

    Abstract

    We consider the seesaw model with two right-handed neutrinos, $N_1$ and $N_2$, the masses of which are hierarchical, and investigate their contribution to the neutrinoless double beta ($0 \nu \beta \beta$) decay. Although the lepton number is broken by the Majorana masses of right-handed neutrinos, such decay processes can be absent in some cases. We present a possibility where the lighter $N_1$ gives a destructive contribution to the decay of active neutrinos by choosing the specific mixing elements of $N_1$, while $N_2$ is sufficiently heavy not to contribute to the $0 \nu \beta \beta$ decay. In this case the mixing elements of $N_1$ in the charged current interaction are determined by its mass and the Majorana phase of active neutrinos. We then study the impacts of such a possibility on the direct search for $N_1$. In addition, we discuss the consequence of the case when the $0 \nu \beta \beta$ decay in one specific nucleus is absent.

    DOI: 10.1093/ptep/ptab046

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    Other Link: http://academic.oup.com/ptep/article-pdf/2021/6/063B01/38694492/ptab046.pdf

  • Neutrino masses and gravitational wave background Reviewed

    Takehiko Asaka, Hisashi Okui

    Physics Letters B   814   136074 - 136074   2021.3

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    Publishing type:Research paper (scientific journal)   Publisher:Elsevier BV  

    DOI: 10.1016/j.physletb.2021.136074

    arXiv

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

    Takehiko Asaka, Hiroyuki Ishida, Kazuki Tanaka

    Physical Review D   103 ( 1 )   2020.12

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    Publishing type:Research paper (scientific journal)   Publisher:American Physical Society (APS)  

    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

    arXiv

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    Other Link: http://arxiv.org/pdf/2012.12564v2

  • Lepton flavor model with modular A4 symmetry in large volume limit Reviewed

    Takehiko Asaka, Yongtae Heo, Takahiro Yoshida

    Physics Letters B   811   135956 - 135956   2020.12

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    Publishing type:Research paper (scientific journal)   Publisher:Elsevier BV  

    DOI: 10.1016/j.physletb.2020.135956

    arXiv

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  • Direct baryogenesis in the broken phase Reviewed

    Takehiko Asaka, Hiroyuki Ishida, Wen Yin

    Journal of High Energy Physics   2020 ( 7 )   2019.12

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    Publishing type:Research paper (scientific journal)   Publisher:Springer Science and Business Media LLC  

    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

    arXiv

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    Other Link: http://arxiv.org/pdf/1912.08797v1

  • Modular $A_4$ invariance and leptogenesis Reviewed

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

    Journal of High Energy Physics   2020 ( 1 )   2019.9

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    Publishing type:Research paper (scientific journal)   Publisher:Springer Science and Business Media LLC  

    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

    arXiv

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    Other Link: http://arxiv.org/pdf/1909.06520v1

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

    Takehiko Asaka, Takahiro Yoshida

    Journal of High Energy Physics   2019 ( 9 )   2018.12

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    Publishing type:Research paper (scientific journal)   Publisher:Springer Science and Business Media LLC  

    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

    arXiv

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    Other Link: http://arxiv.org/pdf/1812.11323v3

  • Tomography by neutrino pair beam Reviewed

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

    Phys.Lett.B   785   536 - 542   2018.10

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    Publishing type:Research paper (scientific journal)  

    DOI: 10.1016/j.physletb.2018.09.004

    Web of Science

    arXiv

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  • Initial condition for baryogenesis via neutrino oscillation Reviewed

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

    PHYSICAL REVIEW D   96 ( 8 )   2017.10

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher: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

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

    Asaka, Takehiko, Hiroyuki Ishida

    Phys.Lett.B   763   393 - 396   2016.12

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher: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

    arXiv

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

    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 PHYSICS   79 ( 12 )   2016.12

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    Language:English   Publisher: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

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  • Reinterpretation of the Starobinsky model Reviewed

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

    PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS   ( 12 )   2016.12

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher: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

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

    Asaka, Takehiko, Eijima, Shintaro, Hiroyuki Ishida

    Phys.Lett.B   762   371 - 375   2016.11

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher: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

    arXiv

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  • Basic oscillation measurables in the neutrino pair beam Reviewed

    T. Asaka, M. Tanaka, M. Yoshimura

    Physics Letters B   760   359 - 364   2016.9

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    Publishing type:Research paper (scientific journal)   Publisher:Elsevier BV  

    DOI: 10.1016/j.physletb.2016.07.001

    arXiv

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  • Probing heavy neutrinos in the COMET experiment Reviewed

    Asaka, Takehiko, Watanabe, Atsushi

    PTEP   2016 ( 3 )   2016.3

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    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

    arXiv

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  • Perturbativity in the seesaw mechanism Reviewed

    Asaka, Takehiko, Tsuyuki, Takanao

    Phys.Lett.B   753   147 - 149   2016.2

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    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

    arXiv

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  • Seesaw mechanism at electron-electron colliders Reviewed

    Takehiko Asaka, Tsuyuki, Takanao

    Phys.Rev.D   92 ( 9 )   094012 - 094012   2015.11

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher: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

    arXiv

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  • Lepton Universality in the $\nu$MSM Reviewed

    Asaka, Takehiko, Eijima, Shintaro, Takeda, Kazuhiro

    Phys.Lett.B   742   303 - 309   2015.3

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    We consider the nu MSM which is an extension of the Standard Model by three right-handed neutrinos with masses below the electroweak scale, in which the origins of neutrino masses, dark matter, and baryon asymmetry of the universe are simultaneously explained. Among three heavy neutral leptons, N-2 and N-3, which are responsible to the seesaw mechanism of active neutrino masses and the baryogenesis via flavor oscillation, can induce sizable contributions to various lepton universality in decays of charged mesons. Then the possible deviations of the universality in the nu MSM are investigated. We find that the deviation in kaon decay can be as large as O(10(-3)), which will be probed in near future experiments. (C) 2015 The Authors. Published by Elsevier B.V.

    DOI: 10.1016/j.physletb.2015.01.049

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    arXiv

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

    Takehiko Asaka, Mikhail Shaposhnikov, Mikko Laine

    JOURNAL OF HIGH ENERGY PHYSICS   ( 2 )   2015.2

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    Language:English   Publisher:SPRINGER  

    DOI: 10.1007/JHEP02(2015)028

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

    Asaka, Takehiko, Eijima, Shintaro

    PTEP   2013 ( 11 )   2013.8

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher: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

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  • Heavy neutrino search in accelerator-based experiments Reviewed

    Takehiko Asaka, Shintaro Eijima, Atsushi Watanabe

    Journal of High Energy Physics   ( 11 )   2013.3

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    DOI: 10.1093/ptep/ptt094

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  • Kinetic Equations for Baryogenesis via Sterile Neutrino Oscillation Reviewed

    Asaka, Takehiko, Eijima, Shintaro, Ishida, Hiroyuki

    JCAP   02 ( 2 )   021 - 021   2012.12

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    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

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    arXiv

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  • Atmospheric Sterile Neutrinos Reviewed

    Asaka, Takehiko, Watanabe, Atsushi

    JHEP   07 ( 7 )   112 - 112   2012.2

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    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

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    arXiv

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  • Mixing of Active and Sterile Neutrinos Reviewed

    Asaka, Takehiko, Eijima, Shintaro, Ishida, Hiroyuki

    JHEP   04 ( 4 )   011 - 011   2011.1

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    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.

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

    Takehiko Asaka, Hiroyuki Ishida

    PHYSICS LETTERS B   692 ( 2 )   105 - 113   2010.8

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    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

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

    Asaka, Takehiko, Nagao, Hiroaki

    Prog.Theor.Phys.   124 ( 2 )   293 - 314   2010.4

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    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

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  • Baryogenesis via Sterile neutrino oscillation and neutrino parameters Reviewed

    Takehiko Asaka, Hiroyuki Ishida

    PROGRESS IN PARTICLE AND NUCLEAR PHYSICS   64 ( 2 )   390 - 392   2010.4

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    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

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

    Asaka, Takehiko, Ishida, Hiroyuki

    Phys.Lett.B   692 ( 2 )   105 - 113   2010.4

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    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.

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  • Leptogenesis with an almost conserved lepton number Reviewed

    Asaka, Takehiko, Blanchet, Steve

    Phys.Rev.D   78 ( 12 )   123527 - 123527   2008.10

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    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.

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

    Asaka, Takehiko, Ishiwata, Koji, Moroi, Takeo

    Phys.Rev.D   75 ( 6 )   065001 - 065001   2007.12

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    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.

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  • Lightest sterile neutrino abundance within the vMSM Reviewed

    Takehiko Asaka, Mikhail Shaposhnikov, Mikko Laine

    JOURNAL OF HIGH ENERGY PHYSICS   ( 1 )   2007.1

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    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.

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  • Lightest sterile neutrino abundance within the vMSM Reviewed

    Takehiko Asaka, Mikhail Shaposhnikov, Mikko Laine

    JOURNAL OF HIGH ENERGY PHYSICS   2007 ( 1 )   091   2007.1

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    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.

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

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

    Takehiko Asaka, Koji Ishiwata, Takeo Moroi

    SUSY06: THE 14TH INTERNATIONAL CONFERENCE ON SUPERSYMMETRY AND THE UNIFICATION OF FUNDAMENTAL INTERACTIONS   903   16 - +   2007

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    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.

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  • Right-handed sneutrino as cold dark matter Reviewed

    Asaka, Takehiko, Ishiwata, Koji, Moroi, Takeo

    Phys.Rev.D   73 ( 5 )   051301 - 051301   2006.12

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    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.

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  • On the hadronic contribution to sterile neutrino production Reviewed

    Asaka, Takehiko, Laine, Mikko, Shaposhnikov, Mikhail

    JHEP   06 ( 6 )   053 - 053   2006.5

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    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.

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    Other Link: http://weblib.cern.ch/abstract?CERN-PH-TH-2006-085

  • Gravitinos from heavy scalar decay Reviewed

    Asaka, Takehiko, Nakamura, Shuntaro, Yamaguchi, Masahiro

    Phys.Rev.D   74 ( 2 )   023520 - 023520   2006.4

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    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.

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  • Opening a new window for warm dark matter Reviewed

    Asaka, Takehiko, Shaposhnikov, Mikhail, Kusenko, Alexander

    Phys.Lett.B   638 ( 5-6 )   401 - 406   2006.2

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    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.

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  • Gravitinos from heavy scalar decay Reviewed

    Takehiko Asaka, Shuntaro Nakamura, Masahiro Yamaguchi

    Physical Review D - Particles, Fields, Gravitation and Cosmology   74 ( 2 )   2006

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    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

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  • The vMSM, dark matter and neutrino masses Reviewed

    T Asaka, S Blanchet, M Shaposhnikov

    PHYSICS LETTERS B   631 ( 4 )   151 - 156   2005.12

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    We investigate an extension of the Minimal Standard Model by right-handed neutrinos (the vMSM) to incorporate neutrino masses consistent with oscillation experiments. Within this theory, the only candidates for dark matter particles are sterile right-handed neutrinos with masses of a few keV. Requiring that these neutrinos explain entirely the (warm) dark matter, we find that their number is at least three. We show that, in the minimal choice of three sterile neutrinos, the mass of the lightest active neutrino is smaller than O(10(-5)) eV, which excludes the degenerate mass spectra of three active neutrinos and fixes the absolute mass scale of the other two active neutrinos. (c) 2005 Elsevier B.V. All rights reserved.

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  • The vMSM, dark matter and baryon asymmetry of the universe Reviewed

    T Asaka, M Shaposhnikov

    PHYSICS LETTERS B   620 ( 1-2 )   17 - 26   2005.7

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    We show that the extension of the standard model by three right-handed neutrinos with masses smaller than the electroweak scale (the vMSM) can explain simultaneously dark matter and baryon asymmetry of the universe and be consistent with the experiments on neutrino oscillations. Several constraints on the parameters of the vMSM are derived. (c) 2005 Elsevier B.V. All rights reserved.

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  • Late reheating, hadronic jets and baryogenesis Reviewed

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

    Phys.Rev.Lett.   92 ( 10 )   101303 - 101303   2004.10

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    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.

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  • Bulk and brane anomalies in six-dimensions Reviewed

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

    Nucl.Phys.B   648 ( 1-2 )   231 - 253   2003.9

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    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.

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  • Quarks and leptons between branes and bulk Reviewed

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

    Phys.Lett.B   563 ( 3-4 )   209 - 216   2003.4

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    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.

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

    Asaka, T.

    Phys.Lett.B   562 ( 3-4 )   291 - 298   2003.4

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    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.

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  • Nonthermal leptogenesis from the heavier Majorana neutrinos Reviewed

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

    Nucl.Phys.B   647 ( 1-2 )   252 - 274   2002.7

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    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.

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  • Exceptional coset spaces and unification in six-dimensions Reviewed

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

    Phys.Lett.B   540 ( 3-4 )   295 - 300   2002.4

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    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.

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  • Affleck-Dine leptogenesis and low scale inflation Reviewed

    Asaka, T.

    Phys.Lett.B   521 ( 3-4 )   329 - 334   2001.10

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    We study Affleck-Dine leptogenesis via the LHu flat direction in supersymmetric theories. We find that the baryon asymmetry is enhanced when the energy scale of the inflation is sufficiently low. Especially, we consider models of low scale inflation in which the Hubble parameter during inflation is comparable to (but slightly larger than) the gravitino mass m(3/2) similar to 1 TeV. The observed cosmological baryon asymmetry is obtained with the lightest neutrino mass m(nu1) similar to 10(-4) eV, if the reheating process is suddenly terminated after inflation. (C) 2001 Elsevier Science B.V. All rights reserved.

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  • Gauge unification in six-dimensions Reviewed

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

    Phys.Lett.B   523 ( 1-2 )   199 - 204   2001.8

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    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.

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  • False vacuum decay after inflation Reviewed

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

    Phys.Lett.B   510 ( 1-4 )   271 - 276   2001.4

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    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.

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  • Affleck-Dine leptogenesis with an ultralight neutrino Reviewed

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

    Phys.Rev.D   62 ( 12 )   123514 - 123514   2000.8

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    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

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  • Leptogenesis in inflationary universe Reviewed

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

    Phys.Rev.D   61 ( 8 )   083512 - 083512   2000.7

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    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

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  • Solving the gravitino problem by axino Reviewed

    Asaka, T., Yanagida, T.

    Phys.Lett.B   494 ( 3-4 )   297 - 301   2000.6

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    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

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  • Initial condition for new inflation in supergravity Reviewed

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

    Phys.Rev.D   61   027303 - 027303   2000.6

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    DOI: 10.1103/PhysRevD.61.027303

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  • Cosmological gravitino problem in gauge mediated supersymmetry breaking models Reviewed

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

    Phys.Lett.B   490 ( 1-2 )   136 - 146   2000.5

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    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

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

    Asaka, T., Yamaguchi, Masahiro

    Phys.Rev.D   59 ( 12 )   125003 - 125003   1999.11

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    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

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

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

    Phys.Lett.B   451 ( 3-4 )   317 - 323   1999.10

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    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

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  • Leptogenesis in inflaton decay Reviewed

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

    Phys.Lett.B   464 ( 1-2 )   12 - 18   1999.6

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    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

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  • Cosmological moduli problem and thermal inflation models Reviewed

    Asaka, T., Kawasaki, M.

    Phys.Rev.D   60 ( 12 )   123509 - 123509   1999.5

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    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

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  • Superheavy dark matter and thermal inflation Reviewed

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

    Phys.Rev.D   60 ( 10 )   103518 - 103518   1999.4

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    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

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  • Cosmological moduli problem in gauge mediated supersymmetry breaking theories Reviewed

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

    Phys.Rev.D   58 ( 8 )   083509 - 083509   1998.11

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    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

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  • Hadronic axion model in gauge mediated supersymmetry breaking Reviewed

    Asaka, T., Yamaguchi, Masahiro

    Phys.Lett.B   437 ( 1-2 )   51 - 61   1998.5

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    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

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

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

    Phys.Rev.D   58 ( 2 )   023507 - 023507   1998.2

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    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

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  • Probing Dynamical Symmetry Breaking Using Top Quark

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

    Progress of Theoretical Physics, Supplement   123 ( 123 )   151 - 161   1996.12

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    Proceedings of YKIS '95

    DOI: 10.1143/PTPS.123.151

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    Other Link: http://dl.ndl.go.jp/info:ndljp/pid/10884197

  • Top-quark mass and isospin breaking in the dynamical symmetry-breaking scenario Reviewed

    T. Asaka, Y. Shobuda, Y. Sumino

    Physical Review D   54 ( 9 )   5698 - 5704   1996.11

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    DOI: 10.1103/physrevd.54.5698

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    Other Link: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.54.5698/fulltext

  • Four fermion decay of Higgs bosons Reviewed

    Asaka, T., Hikasa, Ken-ichi

    Phys.Lett.B   345 ( 1 )   36 - 41   1995.11

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    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

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MISC

  • Precision electroweak shift of muonium hyperfine splitting

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

    2018.10

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    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.

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  • Basic oscillation measurables in the neutrino pair beam

    Asaka Takehiko, Tanaka Minoru, Yoshimura Motohiko

    Meeting Abstracts of the Physical Society of Japan   71   25 - 25   2016

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    DOI: 10.11316/jpsgaiyo.71.2.0_25

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  • Probing Baryon Asymmetry of the Universe by Using Lepton Universality

    Takehiko Asaka, Shintaro Eijima, Kazuhiro Takeda

    2015.6

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    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.

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  • 28aSD-2 Baryogenesis and 0νββ decay in the νMSM

    Asaka Takehiko, Ishida Hiroyuki, Eijima Shintaro

    Meeting Abstracts of the Physical Society of Japan   70   47 - 47   2015

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    DOI: 10.11316/jpsgaiyo.70.2.0_47

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  • 21aSD-11 Dependence of CP violation in the leptonic sector in baryogenesis via neutrino oscillation

    Asaka Takehiko, Ishida Hiroyuki

    Meeting abstracts of the Physical Society of Japan   69 ( 2 )   14 - 14   2014.8

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  • 29pRB-10 Neutrino masses and baryon asymmetry of the universe from light right-handed neutrinos

    Eijima Shintaro, Asaka Takehiko

    Meeting abstracts of the Physical Society of Japan   68 ( 1 )   24 - 24   2013.3

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  • 27pKB-8 Right-handed neutrinos in meson decays

    Eijima Shintaro, Asaka Takehiko, Ishida Hiroyuki

    Meeting abstracts of the Physical Society of Japan   67 ( 1 )   23 - 23   2012.3

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  • 27pKB-9 Momentum Dependence of Density Matrices in Baryogenesis via Neutrino Oscillation

    Asaka Takehiko, Eijima Shintaro, Ishida Hiroyuki

    Meeting abstracts of the Physical Society of Japan   67 ( 1 )   23 - 23   2012.3

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  • 26aGC-10 Neutrino mixing and neutrinoless double beta decay in the νMSM

    Asaka Takehiko, Eijima Shintaro, Ishida Hiroyuki

    Meeting abstracts of the Physical Society of Japan   66 ( 1 )   7 - 7   2011.3

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  • 13pSD-2 Dark Matter Production after Inflation

    Asaka Takehiko, Nagao Hiroaki

    Meeting abstracts of the Physical Society of Japan   65 ( 2 )   9 - 9   2010.8

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  • 23aBV-12 Search for sterile neutrino in pion decay

    Asaka Takehiko, Eijima Shintaro

    Meeting abstracts of the Physical Society of Japan   65 ( 1 )   15 - 15   2010.3

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  • 21pBV-9 Right-handed neutrino from inflaton decay as Dark Matter candidate

    Asaka Takehiko, Nagao Hiroaki

    Meeting abstracts of the Physical Society of Japan   65 ( 1 )   10 - 10   2010.3

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  • 30aVP-12 Baryogenesis via right-handed neutrino oscillation

    Asaka Takehiko, Ishida Hiroyuki

    Meeting abstracts of the Physical Society of Japan   64 ( 1 )   18 - 18   2009.3

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

    T Asaka

    Journal of Physics: Conference Series   120 ( 4 )   042006 - 042006   2008.7

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

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  • 27aXA-2 Right-Handed Snuetrino as Cold Dark Matter

    Asaka Takehiko, Ishiwata Koji, Moroi Takeo

    Meeting abstracts of the Physical Society of Japan   61 ( 1 )   2 - 2   2006.3

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

    Takehiko Asaka, Y. Takanishi

    2004.9

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    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.

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Research Projects

  • 暗黒物質から探る標準模型を超えた新物理

    Grant number:20H01898

    2020.4 - 2024.3

    System name:科学研究費助成事業 基盤研究(B)

    Research category:基盤研究(B)

    Awarding organization:日本学術振興会

    淺賀 岳彦

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    Grant amount:\17160000 ( Direct Cost: \13200000 、 Indirect Cost:\3960000 )

    本研究では、ニュートリノ質量起源の問題を解決する理論として、標準模型に右巻きニュートリノを導入した模型における暗黒物質の実験検証について研究を進めている。今年度は、右巻きニュートリノが暗黒物質となるシナリオを検討し、この暗黒物質を直接検証法により探索可能か研究を進めた。特に、我々の天の川銀河に束縛されている暗黒物質が実験室内の物質と衝突した際、物質(原子核や電子)が得る反跳エネルギーをシグナルにした探索法を検討した。右巻きニュートリノ暗黒物質の質量が10 keV 程度と軽いため、十分な大きさの反跳エネルギーを得るためには、原子中の原子核より束縛電子との散乱に着目する方が良い。そこで、暗黒物質反応による電子反跳エネルギーのスペクトルを求めることにした。
    準備研究として、入射粒子として右巻きニュートリノではなく、通常の左巻きニュートリノの場合を検討した。Roothaan-Hartree-Fock近似に基づく原子中の電子分布を考慮して、電子型左巻きニュートリノとHe, Ne, Xe原子との散乱による反跳エネルギーのスペクトルを求めた。入射エネルギーが低く、標的原子の原子番号が大きくなると束縛の効果による自由電子と比較して散乱断面積が小さくなることがわかった。得られた反跳エネルギーのスペクトルは、暗黒物質の信号の背景事象となるため、貴重な成果となった。上記の準備のもと、現在右巻きニュートリノ暗黒物質による反跳エネルギーのスペクトル、およびシグナル強度の評価を進めている。

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  • 原始重力波を用いたニュートリノ質量獲得機構の解明

    Grant number:19H05097

    2019.4 - 2021.3

    System name:科学研究費助成事業 新学術領域研究(研究領域提案型)

    Research category:新学術領域研究(研究領域提案型)

    Awarding organization:日本学術振興会

    淺賀 岳彦

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    Grant amount:\2340000 ( Direct Cost: \1800000 、 Indirect Cost:\540000 )

    現代物理学における重要課題の一つである素粒子ニュートリノの質量起源について探究した。特に、三世代のうち一番軽いニュートリノの質量を宇宙背景重力波観測から探索する手法を提案した。一番軽い質量は、宇宙背景放射や構造形成の観測、およびベーター崩壊の運動学等により探索されているが、meVスケール以下の大きさについては感度がないため、観測手法の開発が重要な課題となっている。本研究では、右巻きニュートリノを導入したシーソー機構の枠組みでこの問題の解決に挑戦した。
    シーソー機構はニュートリノの極微質量を自然に説明し、さらに暗黒物質や宇宙物質・反物質非対称性の起源も同時に説明するため魅力的な枠組みである。この場合、一番軽い質量が非常に小さくなると、右巻きニュートリノの寿命が非常に長くなり、その崩壊により宇宙の付加的エントロピー生成が生じ宇宙の熱史を大きく変更する可能性がある。一方、重力波は近年その存在が確認され注目を集めている。重力波には天体起源のものと、宇宙誕生直後のインフレーション時の量子揺らぎに起因した背景重力波がある。後者は、インフレーション後の宇宙発展の情報がスペクトルに刻まれており、初期宇宙の情報を運ぶ。本研究では、右巻きニュートリノによる付加的エントロピー生成の痕跡を背景重力波に見出し、ニュートリノ質量を探索する手法を提示した。
    我々は、付加的なエントロピー生成が生じた場合、背景重力波スペクトルが臨界周波数以上で減衰されることに注目した。特に、臨海周波数は一番軽いニュートリノ質量と右巻きニュートリノ質量により決まり、減衰率は一番軽いニュートリノ質量により決まることを見出した。さらに、現在計画されているパルサータイミングアレイやレーザー干渉計による重力波観測による想定感度と比較し、理論が予言する臨海周波数と減衰率の観測が期待できることを示した。

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  • 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

    Grant number:18H03708

    2018.4 - 2023.3

    System name:科学研究費助成事業 基盤研究(A)

    Research category:基盤研究(A)

    Awarding organization:日本学術振興会

    磯 暁, 淺賀 岳彦, 川合 光

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    Grant amount:\43290000 ( Direct Cost: \33300000 、 Indirect Cost:\9990000 )

    (1)階層性問題を解決するための古典的スケール不変性に基づく素粒子模型として、標準模型の拡張を考えると、必然的に電弱対称性が宇宙初期において過冷却を起こし、QCD相転移が引き金となり電弱対称性の破れが発生し、e-folding 5程度の熱的インフレーションが予言される。原始インフレーションとは異なる第二のインフレーションは、それ以前に作られていた粒子密度を大幅に薄めることができ、様々な興味深い現象と関係する。その一つは、過冷却に基づく暗黒物質シナリオであり、もう一つは、QCD相転移で作られたアキシオンポテンシャル生成で、アキシオンの原始ゆらぎが宇宙の曲率ゆらぎに転化され、現在のCMBゆらぎを生成する可能性が考えられる。古典的B-L模型では、等曲率ゆらぎの観測制限との整合性に問題があることが明らかとなった。そこで、初期宇宙で標準模型と全く異なる温度発展をするスカラー場を導入することで、この矛盾を解決する可能性を検討した。
    (2)階層性問題を解決するためのトップダウンアプローチとして、回転Dブレーンを使ったダイナミクスを検討している。2019年度は、回転ブレーンの間に、超対称性が破れた結果働く引力相互作用を計算するための、計算手法(部分的モジュラー変換)を開発した。
    (3)階層性問題に示唆された標準模型のミニマルな拡張模型では、軽い右巻きニュートリノが重要な働きをする。TeV質量を持つ右巻きニュートリノが縮退した質量を持つことで起こるレプトン生成のパラメータ領域とニュートリノを含まない二重ベータ崩壊の実験的制限についての現象論的研究を行い、さらにレプトン質量行列の背後に離散対称性がある時のレプトン生成機構の研究を行なった。
    (4) 階層性原理に基づく古典的スケール不変な模型で、スカラー場が2種類ある時に、くりこみ群を通して電弱スケールをダイナミカルに生成する可能性を検討した。

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  • Search for the origins of dark matter and baryon asymmetry by direct search experiments

    Grant number:17K05410

    2017.4 - 2020.3

    System name:Grants-in-Aid for Scientific Research

    Research category:Grant-in-Aid for Scientific Research (C)

    Awarding organization:Japan Society for the Promotion of Science

    Asaka Takehiko

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    Grant amount:\3510000 ( Direct Cost: \2700000 、 Indirect Cost:\810000 )

    We have investigated the impacts of right-handed neutrinos, which can lead to tiny neutrino masses observed in oscillation experiments through the seesaw mechanism, to the origins of dark matter and baryon asymmetry of the Universe. One of the outcomes is that we have shown that the resonant leptogenesis via TeV scale right-handed neutrinos is successful and its experimental implication to the neutrinoless double beta decays. Second, we have constructed the model for the baryon asymmetry based on the modular symmetry associated with the torus compactification in higher-dimensional theories. Finally, we have considered the neutrino tomography of the earth as one application of neutrino physics.

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  • 電弱スケールでの共鳴レプトン数生成機構

    Grant number:17H05198

    2017.4 - 2019.3

    System name:科学研究費助成事業 新学術領域研究(研究領域提案型)

    Research category:新学術領域研究(研究領域提案型)

    Awarding organization:日本学術振興会

    淺賀 岳彦

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    Grant amount:\1950000 ( Direct Cost: \1500000 、 Indirect Cost:\450000 )

    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].

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  • 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

    Grant number:15H01031

    2015.4 - 2017.3

    System name:科学研究費助成事業 新学術領域研究(研究領域提案型)

    Research category:新学術領域研究(研究領域提案型)

    Awarding organization:日本学術振興会

    淺賀 岳彦

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    Grant amount:\1950000 ( Direct Cost: \1500000 、 Indirect Cost:\450000 )

    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。

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  • 軽い右巻きニュートリノの宇宙物理と実験検証

    Grant number:26105508

    2014.4 - 2016.3

    System name:科学研究費助成事業 新学術領域研究(研究領域提案型)

    Research category:新学術領域研究(研究領域提案型)

    Awarding organization:日本学術振興会

    淺賀 岳彦

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    Authorship:Principal investigator  Grant type:Competitive

    Grant amount:\3510000 ( Direct Cost: \2700000 、 Indirect Cost:\810000 )

    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。

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  • Mechanism for generating baryonic and dark matter in the universe and particle physics model beyond the Standard Model

    Grant number:25400249

    2013.4 - 2017.3

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)

    Research category:Grant-in-Aid for Scientific Research (C)

    Awarding organization:Japan Society for the Promotion of Science

    ASAKA Takehiko

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    Authorship:Principal investigator  Grant type:Competitive

    Grant amount:\4810000 ( Direct Cost: \3700000 、 Indirect Cost:\1110000 )

    We have investigated physics beyond the Standard Model based on the origin of non-zero neutrino masses indicated by oscillation experiments. In particular, a framework in which neutrino masses, cosmic dark matter, and baryon asymmetry of the universe can be explained at the same time has been considered. We have focused on right-handed neutrinos which masses are lighter than the electroweak scale (about 100 GeV) and discussed the mechanism for generating the baryon asymmetry and the methods of the experimental searches for such particles.

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  • The mass and mixing of the sterile neutrino and those phenomenological studies

    Grant number:24654062

    2012.4 - 2015.3

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research

    Research category:Grant-in-Aid for Challenging Exploratory Research

    Awarding organization:Japan Society for the Promotion of Science

    TANIMOTO Morimitsu, ASAKA Takehiko

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    Grant amount:\2600000 ( Direct Cost: \2000000 、 Indirect Cost:\600000 )

    In this work, we have studied the neutrino model phenomenologically by focusing on the mass and the mixing angle of the sterile neutrino.
    The first result: we have built the neutrino model which can explain the active neutrino masses and the large mixing angles with the minimal number of parameters under the assumption of the existence of the sterile neutrino. This model gives us the accurate prediction of the mixing angle θ12, and so it is testable in the future neutrino experiments. The second result: we have found that the CP violation of the neutrinos can be predicted in terms of the violating pattern of the flavor symmetery. These results have been published in the one textbook and 20 papers.
    In addition, we have presented our results as the invited talk at the neutrino conference 2014(Boston, June, 2014).

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  • Particle models based on superconformal dynamics with discrete flavor symmetries

    Grant number:22540269

    2010 - 2012

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)

    Research category:Grant-in-Aid for Scientific Research (C)

    Awarding organization:Japan Society for the Promotion of Science

    NAKANO Hiroaki, TANIMOTO Morimitsu, ASAKA Takehiko, YOSHIOKA Koichi

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    Grant amount:\2860000 ( Direct Cost: \2200000 、 Indirect Cost:\660000 )

    Supersymmetry (SUSY) is an attractive idea for seeking the origin of electroweak symmetry breaking. In this study, we focused on a possible relation between a mechanism for suppressing flavor violating processes and a candidate of dark matter. We examined two different scenarios for the suppression mechanism of flavor violations: The first one is models with superconformal interactions while the second one is models with U(1)R symmetry. Specifically we found relations between R-breaking gravitino mass,generation mechanism of tiny neutrino mass and proton stability.

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  • Flavor Symmetry of Quarks/Leptons and its Verification

    Grant number:21340055

    2009.4 - 2014.3

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

    Research category:Grant-in-Aid for Scientific Research (B)

    Awarding organization:Japan Society for the Promotion of Science

    TANIMOTO Morimitsu, NAKANO Hiroaki, ASAKA Takehiko

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    Grant amount:\18720000 ( Direct Cost: \14400000 、 Indirect Cost:\4320000 )

    In this project, we study the phenomenological consequences in the framework of the non-abelian discrete flavor symmetry. At first, we predict the large two neutrino mixing angles and the reactor angle by using the flavor symmetry. Based on this result, we clarify the flavor structure of the squark and slepton (SUSY particle) as well as quarks/leptons.
    1. The reactor angle theta_13 is predictable in the A4 and S4 flavor symmetries.
    2. We present the analyses of the CP violation of B mesons observed at LHCb. In conclusion, we obtain the flavor structure of squarks.

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  • Construction of unified theory for particle physics describing the evolution of the universe

    Grant number:21540260

    2009 - 2012

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)

    Research category:Grant-in-Aid for Scientific Research (C)

    Awarding organization:Japan Society for the Promotion of Science

    ASAKA Takehiko, TANIMOTO Morimitsu, HIROAKI Nakano

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    Grant type:Competitive

    Grant amount:\4290000 ( Direct Cost: \3300000 、 Indirect Cost:\990000 )

    We have investigated new physics beyond the Standard Model explaining neutrino masses, dark matter and baryon asymmetry of the universe. In particular, the extension by right-handed neutrinos with masses smaller than the electroweak scale has been considered. We have discussed baryogenesis by right-handed neutrino oscillations and the direct searches of right-handed neutrinos.

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  • ニュートリノで探る現在の宇宙像

    Grant number:18740122

    2006 - 2007

    System name:科学研究費助成事業 若手研究(B)

    Research category:若手研究(B)

    Awarding organization:日本学術振興会

    浅賀 岳彦

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    Grant type:Competitive

    Grant amount:\2200000 ( Direct Cost: \2200000 )

    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。

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  • 超対称性に基づく素粒子の統一理論と宇宙物理

    Grant number:99J08791

    1999 - 2000

    System name:科学研究費助成事業 特別研究員奨励費

    Research category:特別研究員奨励費

    Awarding organization:日本学術振興会

    浅賀 岳彦

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    Grant amount:\2400000 ( Direct Cost: \2400000 )

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Teaching Experience (researchmap)

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Teaching Experience

  • 量子研究の最前線

    2023
    Institution name:新潟大学

  • 物理学特論II

    2022
    Institution name:新潟大学

  • 日本事情自然系A

    2021
    Institution name:新潟大学

  • 自然科学総論I

    2021
    Institution name:新潟大学

  • 数理物質科学の最前線

    2021
    Institution name:新潟大学

  • 理学スタディ・スキルズ

    2021
    Institution name:新潟大学

  • 量子力学IIB

    2020
    Institution name:新潟大学

  • 現代物理学セミナーB

    2020
    Institution name:新潟大学

  • 量子力学IIA

    2020
    Institution name:新潟大学

  • 現代物理学セミナーA

    2020
    Institution name:新潟大学

  • 物理学特論II

    2020
    -
    2022
    Institution name:新潟大学

  • 素粒子物理学

    2019
    Institution name:新潟大学

  • 理学スタディ・スキルズ

    2018
    -
    2021
    Institution name:新潟大学

  • 素粒子物理学I

    2017
    Institution name:新潟大学

  • 論文演習

    2015
    Institution name:新潟大学

  • 数理物質科学特定研究Ⅲ(物理学)

    2015
    Institution name:新潟大学

  • 研究発表演習・発表Ⅲ

    2015
    Institution name:新潟大学

  • 数理物質科学演習Ⅲ(物理学)

    2015
    Institution name:新潟大学

  • 理論素粒子物理学III

    2014
    Institution name:新潟大学

  • 量子力学II

    2014
    Institution name:新潟大学

  • 研究発表演習・発表Ⅰ

    2014
    -
    2015
    Institution name:新潟大学

  • 研究発表演習・発表Ⅱ

    2014
    -
    2015
    Institution name:新潟大学

  • 数理物質科学特定研究Ⅱ(物理学)

    2014
    -
    2015
    Institution name:新潟大学

  • 素粒子物理学II

    2013
    -
    2018
    Institution name:新潟大学

  • 数理物質科学特定研究ⅡA(物理学)

    2013
    -
    2015
    Institution name:新潟大学

  • 数理物質科学特定研究ⅡB(物理学)

    2013
    -
    2015
    Institution name:新潟大学

  • 数理物質科学演習Ⅱ(物理学)

    2013
    -
    2015
    Institution name:新潟大学

  • 数理物質科学演習Ⅰ(物理学)

    2013
    -
    2015
    Institution name:新潟大学

  • 数理物質科学特定研究Ⅰ(物理学)

    2013
    -
    2015
    Institution name:新潟大学

  • 現代物理学への招待(物理学学習法)

    2013
    Institution name:新潟大学

  • 物理学基礎A I

    2011
    Institution name:新潟大学

  • 課題探索特講

    2010
    -
    2014
    Institution name:新潟大学

  • 物理学演習

    2010
    Institution name:新潟大学

  • ゲージ場理論特論Ⅲ

    2008
    Institution name:新潟大学

  • 物理数学I

    2008
    -
    2013
    Institution name:新潟大学

  • 対称性とゲージ場理論

    2008
    -
    2013
    Institution name:新潟大学

  • 量子力学演習II

    2007
    Institution name:新潟大学

  • 物理数学演習II

    2007
    -
    2009
    Institution name:新潟大学

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