Shigeki Matsumoto

The University of Tokyo, Edo, Tōkyō, Japan

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Publications (80)135.94 Total impact

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    ABSTRACT: We explore a singlet Majorana fermion dark matter candidate using an effective field theory (EFT) framework, respecting the relations imposed by the standard model $SU(3)_C \times SU(2)_L \times U(1)_Y$ gauge invariance among different couplings. All operators of dimension-5 and dimension-6, forming a complete basis, are taken into account at the same time, keeping in view ultraviolet completions which can give rise to more than one operator at a time. If in addition CP-conservation is assumed, the remaining parameter space, where an EFT description is valid, is found to be rather restricted after imposing constraints from relic abundance, direct, indirect and collider searches. On including the CP-violating dimension-5 operator, $(\overline{\chi}i \gamma_5 \chi) (H^\dagger H)$, a significantly larger parameter space opens up. We use the profile likelihood method to map out the remaining landscape of such a DM scenario. The reach of future searches using ton-scale direct detection experiments, an $e^+ e^-$ collider like the proposed ILC and limits from future gamma-ray observations are also estimated.
    07/2014;
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    ABSTRACT: We discuss the indirect detection of the wino dark matter utilizing gamma-ray observations of dwarf spheroidal galaxies (dSphs). After carefully reviewing current limits with particular attention to astrophysical uncertainties, we show prospects of the wino mass limit in future gamma-ray observation by the Fermi-LAT and the GAMMA-400 telescopes. We find that the improvement of the so-called $J$-factor of both the classical and the ultra-faint dSphs will play a crucial role to cover whole mass range of the wino dark matter. For example, with $\delta (\log_{10}J) = 0.1$ for both the classical and the ultra-faint dSphs, whole wino dark matter mass range can be covered by 15 years and 10 years data at the Fermi-LAT and GAMMA-400 telescopes, respectively.
    05/2014;
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    ABSTRACT: The large value of the tensor-to-scalar ratio in the cosmic microwave background radiation reported by the BICEP2 collaboration gives strong impact on models of supersymmetry (SUSY). The large ratio indicates inflation with a high-energy scale and thus a high reheating temperature in general, and various SUSY models suffer from the serious gravitino and Polonyi problems. In this article, we discuss a class of the high-scale SUSY breaking models which are completely free from those problems. With especially focusing on the dark matter relic abundance, we examine how the BICEP2 result narrows down the parameter space of the models, assuming the simplest chaotic inflation model. We find that the mass of the dark matter is predicted to be less than about 1 TeV thanks to the non-thermal production in the early universe through the decay of abundant gravitinos produced after the reheating process. We also discuss implications in some details to dark matter searches at collider and indirect dark matter detection experiments.
    03/2014;
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    Keisuke Harigaya, Kunio Kaneta, Shigeki Matsumoto
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    ABSTRACT: The high-scale supersymmetry (SUSY) breaking scenario is now attracting many attentions, because it is consistent with almost all experiments of particle physics, astrophysics, and cosmology performed so far: e.g. it is possible to explain the Higgs mass of about 126GeV and contains WIMP dark matter candidates. In the scenario, gauginos are predicted to be around the TeV scale, and thus within a kinematically accessible range of near future experiments. Calculation of the thermal relic abundance for gaugino (bino or wino) dark matter is then of particular importance in order to clarify its mass consistent with cosmology and to determine future directions for exploring the high-scale SUSY breaking scenario. In this article, we calculate the abundance of the gaugino dark matter, with especially focusing on various coannihilations between gauginos, which has not been extensively studied so far. Our calculation involves the Sommerfeld effect on wino and gluino annihilations, which is known to give significant contributions to their cross sections. Based on obtained results, we discuss some implications to gaugino searches at collider and indirect detection experiments of dark matter.
    03/2014;
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    Masahiro Ibe, Shigeki Matsumoto, Tsutomu T. Yanagida
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    ABSTRACT: The observed Higgs boson mass poses a new puzzle in addition to the longstanding problem of the origin of the electroweak scale; the shallowness of the Higgs potential. The Higgs quartic coupling even seems to vanish at around the Planck scale within the uncertainties of the top quark mass and the strong gauge coupling. We show that the shallowness of the Higgs potential might be an outcome of supersymmetry breaking at around the Planck scale. There, the electroweak fine-tuning in the Higgs quadratic terms leads to an almost vanishing quartic coupling at around the Planck scale.
    Physics Letters B. 12/2013; 732.
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    Masahiro Ibe, Ayuki Kamada, Shigeki Matsumoto
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    ABSTRACT: We study phenomenological aspects of the bino-wino co-annihilation scenario in high-scale supersymmetry breaking models. High-scale SUSY breaking scenarios are considered to be promising possibility after the discovery of the Higgs boson with a mass around 126 GeV. In this paper, we discuss the bino lightest supersymmetric particle (LSP) accompanied by the at most around 30 GeV heavier wino. With the suitable mass splitting between the bino and the wino, the bino LSP has the correct relic abundance of dark matter. For the smaller mass splitting, the late-time decay of the gravitino can provide the correct abundance of the bino dark matter. It is extremely challenging to find signals from the bino dark matter in direct and indirect detections. By utilizing multi-jets plus missing transverse momentum events at the LHC, we can constraint the gluino mass and thus probe the bino-wino co-annihilation scenario indirectly. The collider experiment, however, can not search the bino dark matter directly. In this paper, we suggest the direct probe of the bino dark matter. We show that the bino dark matter leaves imprints on the small-scale matter power spectrum when the bino dark matter is produced by the decay of the gravitino. The non-thermal bino dark matter behaves as mixed (cold+warm) dark matter.
    11/2013;
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    ABSTRACT: Asymmetric dark matter (ADM) has been an attractive possibility attempting to explain the observed ratio of baryon to dark matter abundance in the universe. While a bosonic ADM is constrained by the limits from existence of old neutron stars, a fermionic ADM requires an additional light particle in order to annihilate its symmetric component in the early universe. We revisit the phenomenology of a minimal GeV scale fermionic ADM model including a light scalar state. The current constraints on this scenario from cosmology, dark matter direct detection, flavour physics and collider searches are investigated in detail. We estimate the future reach on the model parameter space from next-generation dark matter direct detection experiments, Higgs boson property measurements and search for light scalars at the LHC, as well as the determination of Higgs invisible branching ratio at the proposed ILC.
    Journal of High Energy Physics 06/2013; · 5.62 Impact Factor
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    ABSTRACT: The AMS-02 collaboration has recently reported an excess of the cosmic-ray positron fraction, which turned out to be consistent with previous results reported by the PAMELA and Fermi-LAT collaborations. A decaying dark matter with the mass around 1 TeV can be responsible for the excess of the positron fraction when it is interpreted as a dark matter signal. Interestingly, the pure gravity mediation model provides such a dark matter, namely an almost pure neutral wino dark matter, when a tiny R-parity violation through $LLE^c$ interactions is introduced. We show that the decaying wino dark matter well reproduces the energy spectrum of the fraction with being consistent with constraints from cosmic-ray anti-proton and gamma-ray observations.
    Journal of High Energy Physics 05/2013; 2013(7). · 5.62 Impact Factor
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    ABSTRACT: The AMS-02 collaboration has recently reported an excess of cosmic-ray positron fractions, which is consistent with previous results at PAMELA and Fermi-LAT experiments. The result indicates the existence of new physics phenomena to provide the origin of the energetic cosmic-ray positron. We pursue the possibility that the enhancement of the positron fraction is due to the decay of gravitino dark matter. We discuss that such a scenario viably fits into the models in which the soft SUSY breaking parameters are dominantly from gauge-mediation mechanism with superparticle masses of around 10 TeV. Our scenario is compatible with ~126 GeV Higgs boson, negative searches for SUSY particles, and non-observation of anomalous FCNC processes. We also point out that the scenario will be tested in near future by measuring the electric dipole moment of the electron and the lepton flavor violating decay of the muon.
    04/2013;
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    ABSTRACT: A monochromatic line in the cosmic neutrino spectrum would be a smoking gun signature of dark matter. It is intriguing that the IceCube experiment has recently reported two PeV neutrino events with energies that may be equal up to experimental uncertainties, and which have a probability of being a background fluctuation estimated to be less than a percent. Here we explore prospects for these events to be the first indication of a monochromatic line signal from dark matter. While measurable annihilation signatures would seem to be impossible at such energies, we discuss the dark matter quantum numbers, effective operators, and lifetimes which could lead to an appropriate signal from dark matter decays. We will show that the set of possible decay operators is rather constrained, and will focus on several viable candidates which could explain the IceCube events; R-parity violating gravitinos, hidden sector gauge bosons, and singlet fermions in an extra dimension. In essentially all cases we find that a PeV neutrino line signal from dark matter would be accompanied by a potentially observable continuum spectrum of neutrinos rising towards lower energies.
    Physical review D: Particles and fields 03/2013; 88(1).
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    ABSTRACT: Here, we give a broad overview of the more natural spectra allowed by the LHC when UDD R-parity violation is allowed. Because R-parity violation removes the missing energy signals in colliders, the experimental constraints on the gluino, stops, sbottoms and higgsinos are relatively mild. We also show that UDD R-parity violation and lepton number conservation can be made consistent with grand unification. This feat is achieved through the product unification, SU(5) X U(3). In this model, mixing of the SM quarks with additional quark like particles charged under the U(3) generate a UDD R-parity violating operator. Furthermore, these models are also capable of generating a "natural" spectra. The emergence of these more natural low-scale spectra relies heavily on the fact that the gaugino masses are non-universal, a natural consequence of product unification.
    Physical review D: Particles and fields 01/2013; 87(11).
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    Masahiro Ibe, Shigeki Matsumoto, Ryosuke Sato
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    ABSTRACT: The recent result of the higgs search at the LHC experiment has lead to more attention to the supersymmetric standard models with heavy sfermions. Among them, the models with the almost pure wino being the lightest supersymmetric particle (LSP) have been widely discussed due to their success in providing a consistent dark matter candidate. The notable phenomenological feature of the wino LSP is the degeneracy with its charged SU(2)_L partner (the charged wino) in mass. The tiny mass splitting makes the charged wino long-lived, which allows us to detect the wino production at the LHC experiment by searching for the disappearing charged tracks inside the detectors. Since the reach of the experiment is sensitive to the mass splitting, it is mandatory to estimate it very precisely. We therefore perform a full calculation of the mass splitting at two-loop level, and find that the splitting is reduced by a few MeV compared to the one-loop calculation. This reduction leads to about a 30 % longer lifetime of the charged wino, with which the current constraint on the wino mass by the ATLAS experiment is improved by about 10 %.
    Physics Letters B 12/2012; 721(s 4–5). · 4.57 Impact Factor
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    ABSTRACT: Present and future expected limits on interactions between dark matter and various quarks are thoroughly investigated in a model-independent way. In particular, the constraints on the interactions from the Large Hadron Collider (LHC) experiment are carefully considered with focusing on mono jet + missing transverse energy, mono b-jet + missing transverse energy, and top quark(s) + missing transverse energy channels. Model-independent upper limits (expected limits) on the cross section times acceptance for non-standard model events are derived at 7 TeV (8 or 14 TeV) running of the LHC experiment. With assuming that the dark matter is a singlet real scalar or a singlet Majorana fermion, we also put constraints on several operators describing its interactions with up, down, strange, charm, bottom and top quarks. These constraints are compared to those obtained by cosmological and astrophysical observations of the dark matter.
    Journal of High Energy Physics 12/2012; 2013(4). · 5.62 Impact Factor
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    ABSTRACT: In the framework of gauge mediation models, we investigate scenarios with heavy squarks and light sleptons, motivated by the recent discovery of the Higgs boson and the deviation of the muon anomalous magnetic moment (g-2) from the SM prediction. We show that only models with a messenger multiplet in the adjoint representation of SU(5) GUT gauge group are the unique possibility that sleptons are light enough to explain the muon g-2 in the minimal setup. We also show that, if there is an additional source of the Higgs soft masses, the muon g-2 can be explained with messenger multiples in the fundamental representation of SU(5) with the help of the light higgsino. Some phenomenological aspects of these models are also discussed.
    Journal of High Energy Physics 10/2012; 2013(3). · 5.62 Impact Factor
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    Masahiro Ibe, Ayuki Kamada, Shigeki Matsumoto
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    ABSTRACT: We study how "warm" the wino dark matter is when it is non-thermally produced by the decays of the gravitino in the early Universe. We clarify the energy distribution of the wino at the decay of the gravitino and the energy loss process after their production. By solving the Boltzmann equation, we show that a sizable fraction of the wino dark matter can be "warm" for the wino mass m_{\tilde w} \sim 100-500 GeV. The "warmness" of the wino dark matter leaves imprints on the matter power spectra and may provide further insights on the origin of dark matter via the future 21 cm line survey. Our calculations can be applied to other non-thermal wino production scenarios such as the wino dark matter produced by the decay of the moduli fields.
    Physical review D: Particles and fields 09/2012; 87(6).
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    ABSTRACT: Supersymmetric theories which can allow for a 125 GeV Higgs mass and also solve the naturalness and susy flavor problems now require a fair degree of complexity. Here we consider the simplest possibility for supersymmetry near the weak scale, but with the requirement of naturalness dropped. In "pure gravity mediation", all supersymmetric particles except for the gauginos lie at tens to thousands of TeV, with the gauginos obtaining loop suppressed masses automatically by anomaly mediation and higgsino threshold corrections. The gauginos are the lightest superpartners, and we investigate the current collider constraints on their masses, as well as the future reach of the LHC. We consider gluino pair production with a jets + missing energy signature, as well as events with disappearing charged tracks caused by charged winos decaying into their neutral partners. We show that presently, gluino masses less than about 1 TeV and wino masses less than about 300 GeV are excluded, and that the 14 TeV LHC can probe gluino masses up to about 2 TeV and wino masses up to 1 TeV.
    Physical review D: Particles and fields 07/2012; 87(1).
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    Masahiro Ibe, Shigeki Matsumoto, Tsutomu T. Yanagida
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    ABSTRACT: Recently, the ATLAS and CMS collaborations reported exciting hints of a standard model-like Higgs boson with a mass around 125 GeV. Such a Higgs boson mass can be easily obtained in the minimal supersymmetric standard model based on the “pure gravity mediation model” where the sfermion masses and the Higgs mass parameters are in the tens to hundreds TeV range, while the gauginos are in the hundreds GeV to TeV range. In this paper, we discuss details of the gaugino mass spectrum in the pure gravity mediation model. We also discuss the signals of the model at current and future experiments such as cosmic-ray observations and the LHC experiments. In particular, we show that the parameter space which is consistent with the thermal leptogenesis can be fully surveyed experimentally in the foreseeable future.
    Physical review D: Particles and fields 05/2012;
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    ABSTRACT: Vector-like quarks are introduced in various new physics models beyond the standard model (SM) at the TeV scale. We especially consider the case that the quark is singlet (triplet) under the SU(2)$_L$ (SU(3)$_c$) gauge group and couples only to the third generation quarks of the SM. The vector-like quark of this kind is often called a top partner. The top partoner $t_p$ decays into $bW, tZ$ and $th$. In the ATLAS and CMS collaborations, the top partner has been searched in the final states of $bW$ and $tZ$, while the search based on the decay mode $t_p\to th$ has not been started yet. However, the decay into $th$ is important since it is significantly enhanced if some strong dynamics exists in the TeV scale. In the presence of a light higgs boson, the decay mode $t_p\to th$ followed by $h\to b\bar{b}$ produces three bottom quarks. We study the sensitivity for the top partner using multi-b-jet events at the 8 TeV run of the LHC experiment. The multi-b-jet eventss turn out to play a complementary role to the existing $t_p\rightarrow bW$ and $tZ$ searches by the ATLAS and CMS collaborations.
    Physical review D: Particles and fields 04/2012; 86(1).
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    ABSTRACT: The Littlest Higgs with T-parity Model (LHT) is one of the attractive candidates of physics beyond the Standard Model. In this study we focus on heavy gauge bosons and heavy leptons that LHT imposes, which are detectable at ILC. The mass and couplings of these particles possess important information of the model's mass generation mechanism and how they interact with other particles. Precision measurement will be essential among verifying the model. We will address the measurement accuracy of Little Higgs particle masses, couplings and model parameters at ILC.
    03/2012;
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    ABSTRACT: Comprehensive analysis on the light Higgs scenario of the minimal supersymmetric standard model is performed in the framework of the non-universal Higgs mass model (NUHM). The NUHM is known to be the simplest framework realizing the light Higgs scenario with the unifications of gaugino and sfermion masses at the scale of grand unified theory being consistent. All important constraints from collider experiments, flavor-changing processes, and cosmological observations are considered in order to clarify the allowed region of the model parameter space, where the Markov Chain Monte Carlo method is used to obtain the region. We show that the region is excluded by current LHC results for the SUSY particle searches. We discuss possible extensions to save the LHS. Even with such extensions, the measurement of B_s to mu^+ mu^- would enable us to test the LHS in the near future.
    Physical review D: Particles and fields 02/2012; 86(1).

Publication Stats

1k Citations
135.94 Total Impact Points

Institutions

  • 2004–2013
    • The University of Tokyo
      • • Institute for the Physics and Mathematics of the Universe (IPMU)
      • • Institute for Cosmic Ray Research
      Edo, Tōkyō, Japan
  • 2007–2011
    • University of Toyama
      Тояма, Toyama, Japan
    • Tohoku University
      • Department of Physics
      Sendai, Kagoshima-ken, Japan
  • 2010
    • University of Alabama
      • Department of Physics and Astronomy
      Tuscaloosa, AL, United States
  • 2005–2007
    • Saitama University
      • Department of Physics
      Saitama, Saitama, Japan