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Junji Hisano

Publications and source records attributed to Junji Hisano.

At least 73 records · Page 4Linked to original sources
arXiv2010

WIMP dark matter in gauge-mediated SUSY breaking models and its phenomenology

We propose an extended version of the gauge-mediated SUSY breaking models where extra $SU(2)_L$ doublets and singlet field are introduced. These fields are assumed to be parity-odd under an additional matter parity. In this model, the lightest parity-odd particle among them would be dark matter in the Universe. In this paper, we discuss direct detection of the dark matter and the collider signatures of the model

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arXiv2010

A complete calculation for direct detection of Wino dark matter

In the anomaly-mediated supersymmetry (SUSY) breaking scenario, neutral gaugino of SU(2)_L multiplet, Wino, can be the lightest SUSY particle and become a candidate for dark matter. We calculated scattering cross section of Wino dark matter with nucleon, which is responsible for direct detection of the dark matter, on the assumption that the SUSY particles and the heavier Higgs bosons have masses of the order of the gravitino mass in the SUSY standard model. In such a case, the Wino-nucleon coupling is generated by loop processes. We have included two-loop contribution to Wino-gluon interaction in the calculation, since it is one of the leading contributions to the Wino-nucleon coupling. It was found that the spin-independent scattering cross section with proton is 10^-(46-48) cm^2. While it is almost independent of the Wino mass, the result is quite sensitive to the Higgs boson mass due to the accidental cancellation.

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arXiv2010

Implications of CDMS II result on Higgs sector in the MSSM

We study implications of two dark matter candidate events at CDMS-II on the neutralino dark matter scenario in the supersymmetric standard model, in light of the recent lattice simulation on the strange quark content of a nucleon. The scattering rate of neutralino-nucleon is dominated by Higgs exchange processes and the mass of heavy Higgs boson is predicted for the neutralino of Bino-Higgsino mixing state. In the case of Wino-Higgsino mixing, the Higgs sector may not be constrained.

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arXiv2009

Positron/Gamma-Ray Signatures of Dark Matter Annihilation and Big-Bang Nucleosynthesis

The positron excess observed by the PAMELA experiment may come from dark matter annihilation, if the annihilation cross section is large enough. We show that the dark matter annihilation scenarios to explain the positron excess may also be compatible with the discrepancy of the cosmic lithium abundances between theory and observations. The wino-like neutralino in the supersymmetric standard model is a good example for it. This scenario may be confirmed by Fermi satellite experiment.

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arXiv2009

Cosmic Rays from Dark Matter Annihilation and Big-Bang Nucleosynthesis

Recent measurements of cosmic-ray electron and positron fluxes by PAMELA and ATIC experiments may indicate the existence of annihilating dark matter with large annihilation cross section. We show that the dark matter annihilation in the big-bang nucleosynthesis epoch affects the light element abundances, and it gives stringent constraints on such annihilating dark matter scenarios for the case of hadronic annihilation. Constraints on leptonically annihilating dark matter models are less severer.

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arXiv2009

Upward muon signals at neutrino detectors as a probe of dark matter properties

We study upward muon flux at neutrino detectors such as Super-Kamiokande resulting from high-energy neutrinos produced by the dark matter annihilation/decay at the Galactic center. In particular, we distinguish showering and non-showering muons as their energy loss processes inside the detector, and show that this information is useful for discriminating dark matter models.

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arXiv2009

Discriminating Electroweak-ino Parameter Ordering at the LHC and Its Impact on LFV Studies

Current limit on the dark matter relic abundance may suggest that $|μ|$ should be smaller than prediction in the minimal supergravity scenario (mSUGRA) for moderate $m_0$ and $m_{1/2}$. The electroweak-ino parameter $M_1, M_2$ and $|μ|$ are then much closer to each other. This can be realized naturally in the non-universal Higgs mass model (NUHM). Since the heaviest neutralino ($\tildeχ^0_4$) and chargino ($\tildeχ^\pm_2$) have significant gaugino components, they may appear frequently in the left-handed squark decay and then be detectable at the LHC. In such a case, we showed that the hierarchy of $M_1, M_2$ and $|μ|$ can be determined. In the light slepton mass scenario with non-vanishing lepton-flavor violation (LFV) in the right-handed sector, NUHM with small $|μ|$ corresponds to region of parameter space where strong cancellation among leading contributions to $Br(μ\to eγ)$ can occur. We showed that determination of electroweak-ino hierarchy plays a crucial role in resolving cancellation point of $Br(μ\to eγ)$ and determination of LFV parameters. We also discussed test of the universality of the slepton masses at the LHC and the implications to SUSY flavor models.

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arXiv2009

A Realistic Extension of Gauge-Mediated SUSY-Breaking Model with Superconformal Hidden Sector

The sequestering of supersymmetry (SUSY) breaking parameters, which is induced by superconformal hidden sector, is one of the solutions for the mu/B_mu problem in gauge-mediated SUSY-breaking scenario. However, it is found that the minimal messenger model does not derive the correct electroweak symmetry breaking. In this paper we present a model which has the coupling of the messengers with the SO(10) GUT-symmetry breaking Higgs fields. The model is one of the realistic extensions of the gauge mediation model with superconformal hidden sector. It is shown that the extension is applicable for a broad range of conformality breaking scale.

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arXiv2009

Neutrino Signals from Annihilating/Decaying Dark Matter in the Light of Recent Measurements of Cosmic Ray Electron/Positron Fluxes

The excess of cosmic-ray electron and positron fluxes measured by the PAMELA satellite and ATIC balloon experiments may be interpreted as the signals of the dark matter annihilation or decay into leptons. In this letter we show that the dark matter annihilation/decay which reproduces the electron/positron excess may yield a significant amount of high-energy neutrinos from the Galactic center. In the case, future kilometer-square size experiments may confirm such a scenario, or even the Super-Kamiokande results already put constraints on some dark matter models.

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arXiv2008

A Complete Analysis of "Flavored" Electric Dipole Moments in Supersymmetric Theories

The Standard Model predictions for the hadronic and leptonic electric dipole moments (EDMs) are well far from the present experimental resolutions, thus, the EDMs represent very clean probes of New Physics effects. Especially, within supersymmetric frameworks with flavor-violating soft terms large and potentially visible effects to the EDMs are typically expected. In this work, we systematically evaluate the predictions for the EDMs at the beyond-leading-order (BLO). In fact, we show that BLO contributions to the EDMs dominate over the leading-order (LO) effects in large regions of the supersymmetric parameter space. Hence, their inclusion in the evaluation of the EDMs is unavoidable. As an example, we show the relevance of BLO effects to the EDMs for a SUSY $SU(5)$ model with right-handed neutrinos.

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arXiv2008

CP Violation in B_s Mixing in the SUSY SU(5) GUT with Right-handed Neutrinos

It is recently announced by the {\bf Ut}{\it fit} collaboration that the CP phase of the $B_s$ mixing amplitude, $ϕ_{B_s}$, deviates more than $3 σ$ from the standard-model prediction. In this paper we discuss how large correction to $ϕ_{B_s}$ is possible in the supersymmetric SU(5) ground unified model (SUSY SU(5) GUT) with right-handed neutrinos. Here, we assume the supergravity-like boundary condition for the SUSY-breaking terms. We found that the 95% probability region derived by the {\bf Ut}{\it fit} collaboration is marginal in this model.

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arXiv2008

Upperbound on Squark Masses in Gauge-Mediation Model with Light Gravitino

We examine stabilities of our supersymmetry-breaking false vacuum in a low-energy direct gauge mediation model of SUSY breaking. The stability required in the high-temperature early universe leads to upperbounds on masses of squarks and gluino as m_\tilde{q} \lesssim 1 TeV and m_\tilde{g} \lesssim 1 TeV for the light gravitino of mass m_{3/2} \lesssim 16 eV.

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arXiv2007

Revisiting Signature of Minimal Gauge Mediation

We revisit phenomenology of the minimal gauge-mediated model. This model is motivated from the SUSY CP and flavor problems. A specific feature of this model is that \tanβis naturally large, since the B term in the Higgs potential is zero at the messenger scale. This leads to significant SUSY contributions to various low-energy observables. We evaluate the anomalous magnetic moment of the muon and the branching ratio of \bar{B}\to X_sγtaking account of recent theoretical and experimental developments. We find that the current experimental data prefer a low messenger scale (\sim 100 TeV) and gluino mass around 1 TeV. We also calculate the branching ratios of \bar{B}\to X_s l^+l^-, B_s\to μ^+μ^-, and B^-\to τ^- \barν, and show that these observables are strongly correlated with each other in this model.

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arXiv2007

Stability of Metastable Vacua in Gauge Mediated SUSY Breaking Models with Ultra Light Gravitino

Recently Murayama and Nomura proposed a simple scheme to construct the gauge mediation models, using metastable supersymmetry breaking vacua. It has a possibility to predict the ultra light gravitino mass m_{3/2} \lesssim 16 eV, while such a light gravitino may destabilize the metastable vacua. We investigate stability of the metastable vacuum of their model. The transition rate from the false vacuum to true ones is evaluated by numerical calculation, including the Coleman-Weinberg potential destabilizing the metastable vacuum. It is found that when the messenger sector is minimal, stability of the metastable vacuum imposes an upperbound on squark mass M_{\tilde q} for the ultra light gravitino as M_{\tilde q} \lesssim 1800 GeV at most. Squarks with this mass may be found in the LHC experiments.

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arXiv2006

Electric Dipole Moments in PseudoDirac Gauginos

The SUSY CP problem is one of serious problems in construction of realistic supersymmetric standard models. We consider the problem in a framework in which adjoint chiral multiplets are introduced and gauginos have Dirac mass terms induced by a U(1) gauge interaction in the hidden sector. This is realized in hidden sector models without singlet chiral multiplets, which are favored from a recent study of the Polonyi problem. We find that the dominant contributions to electron and neutron electric dipole moments (EDMs) in the model come from phases in the supersymmetric adjoint mass terms. When the supersymmetric adjoint masses are suppressed by a factor of \sim 100 compared with the Dirac ones, the electron and neutron EDMs are suppressed below the experimental bound even if the SUSY particle masses are around 1 TeV. Thus, this model works as a framework to solve the SUSY CP problem.

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arXiv2006

Constraining SuperWIMPy and Warm Subhalos with Future Submillilensing

We propose to observe QSO-galaxy strong lens systems to give a new constraint on the damping scale of the initial fluctuations. We find that the future observation of submilliarc scale astrometric shifts of the multiple lensed images of QSOs would find \sim 10^{(3-9)} M_{\odot} subhalos inside the macrolens halo. The superweakly interacting massive particles (superWIMPs) produced from a WIMP decay and the warm dark matter (WDM) particles that predict a comoving damping scale larger than \sim 2 kpc can be constrained if \sim 10^3 M_{\odot} subhalos are detected.

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arXiv2006

Non-perturbative Effect on Thermal Relic Abundance of Dark Matter

We point out that thermal relic abundance of the dark matter is strongly altered by a non-perturbative effect called the Sommerfeld enhancement, when constituent particles of the dark matter are non-singlet under the SU(2)_L gauge interaction and much heavier than the weak gauge bosons. Typical candidates for such dark matter particles are the heavy wino- and higgsino-like neutralinos. We investigate the non-perturbative effect on the relic abundance of dark matter for the wino-like neutralino as an example. We show that its thermal abundance is reduced by 50% compared to the perturbative result. The wino-like neutralino mass consistent with the observed dark matter abundance turns out to be 2.7 TeV < m < 3.0 TeV.

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