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Junji Hisano

Publications and source records attributed to Junji Hisano.

At least 91 records · Page 5Linked to original sources
arXiv2006

New Two-loop Contributions to Hadronic EDMs in the MSSM

Flavor-changing terms with CP-violating phases in the quark sector may contribute to the hadronic electric dipole moments (EDMs). However, within the Standard Model (SM), the source of CP violation comes from the unique CKM phase, and it turns out that the EDMs are strongly suppressed. This implies that the EDMs are very sensitive to non-minimal flavor violation structures of theories beyond the SM. In this paper, we discuss the quark EDMs and CEDMs (chromoelectric dipole moments) in the MSSM with general flavor-changing terms in the squark mass matrices. In particular, the charged-Higgs mediated contributions to the down-quark EDM and CEDM are evaluated at two-loop level. We point out that these two-loop contributions may dominate over the one-loop induced gluino or Higgsino contributions even when the squark and gluino masses are around few TeV and \tanβis moderate.

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arXiv2006

Heavy Wino-like Neutralino Dark Matter Annihilation into Antiparticles

The lightest neutralino is a viable dark matter (DM) candidate. In this paper we study indirect detection of the wino-like neutralino DM using positrons and antiprotons from the annihilation in the galactic halo. When the mass is around 2 TeV, which is favored from the thermal relic abundance, the non-perturbation effect significantly enhances the annihilation cross sections into positrons and antiprotons. We find that the positron and antiproton fluxes with energies larger than 100 GeV may become larger than the expected backgrounds. Since the positron flux is less sensitive to the astrophysical parameters, the detection may be promising in the upcoming experiments such as PAMELA and AMS-02. We also find the wino-like neutralino DM with mass around 2 TeV is compatible with the HEAT anomaly.

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arXiv2006

Investigation of Possible Dark Matter Direct Detection in Electron Accelerators

We investigate a possibility of neutralino dark matter (DM) direct detection in the future electron accelerators. That is counting of high p_T electron recoil events by neutralinos in halo. If selectron and neutralino masses would be precisely measured in future collider experiments, the beam energy could be tuned so that the scatterings are dominated by on-pole selectron exchange. When selectron and neutralino mass difference is smaller than O(10) GeV, the elastic cross section exceeds over micro barn. Discovery of the high p_T electron events would be a firm prove of the neutralino DM component in halo. In the experiment, the electron beam energy must be tuned within O(10) MeV and the electron beam with high currents of O(100)A is required for the detectors of the total length of a few hundred meters so that the sufficient event rate is obtained. The dependence of the event rate on the DM velocity distribution in halo is also discussed. This method might be applicable to other DM candidates.

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arXiv2005

Hadronic EDM Constraints on Orbifold GUTs

We point out that the null results of the hadronic electric dipole moment (EDM) searches constrain orbifold grand unified theories (GUTs), where the GUT symmetry and supersymmetry (SUSY) are both broken by boundary conditions in extra dimensions and it leads to rich fermion and sfermion flavor structures. A marginal chromoelectric dipole moment (CEDM) of the up quark is induced by the misalignment between the CP violating left- and right-handed up-type squark mixings, in contrast to the conventional four-dimensional SUSY GUTs. The up quark CEDM constraint is found to be as strong as those from charged lepton flavor violation (LFV) searches. The interplay between future EDM and LFV experiments will probe the structures of the GUTs and the SUSY breaking mediation mechanism.

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arXiv2005

Non-Perturbative Effect on Dark Matter Annihilation and Gamma Ray Signature from Galactic Center

Detection of gamma rays from dark matter annihilation in the galactic center is one of the feasible techniques to search for dark matter. We evaluate the gamma ray flux in the case that the dark matter has an electroweak SU(2)_L charge. Such dark matter is realized in the minimal supersymmetric standard model (MSSM) when the lightest SUSY particle is the Higgsino- or Wino-like neutralino. When the dark matter is heavy compared to the weak gauge bosons, the leading-order calculation of the annihilation cross sections in perturbation breaks down due to a threshold singularity. We take into account non-perturbative effects by using the non-relativistic effective theory for the two-body states of the dark matter and its SU(2)_L partner(s), and evaluate precise cross sections relevant to the gamma ray fluxes. We find that the annihilation cross sections may be enhanced by several orders of magnitude due to resonances when the dark matter mass is larger than 1 TeV. Furthermore, the annihilation cross sections in the MSSM may be changed by factors even when the mass is about 500 GeV. We also discuss sensitivities to gamma ray signals from the galactic center in the GLAST satellite detector and the large Air Cerenkov Telescope arrays.

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arXiv2005

Direct Detection of the Wino- and Higgsino-like Neutralino Dark Matters at One-Loop Level

The neutralino-nucleon (\tildeχ^0-N) scattering is an important process for direct dark matter searches. In this paper we discuss one-loop contributions to the cross section in the wino-like and Higgsino-like LSP cases. The neutralino-nucleon scattering mediated by the Higgs \tildeχ^0\tildeχ^0 and Z\tildeχ^0\tildeχ^0 couplings at tree level is suppressed by the gaugino-Higgsino mixing at tree level when the neutralino is close to a weak eigenstate. The one-loop contribution to the cross section, generated by the gauge interaction, is not suppressed by any SUSY particle mass or mixing in the wino- and Higgsino-like LSP cases. It may significantly alter the total cross section when σ_{\tildeχ^0 N}\sim 10^{-45} cm^2 or less.

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arXiv2004

Hadronic EDMs in SUSY SU(5) GUTs with Right-handed Neutrinos

We discuss hadronic EDM constraints on the neutrino sector in the SUSY SU(5) GUT with the right-handed neutrinos. The hadronic EDMs are sensitive to the right-handed down-type squark mixings, especially between the second and third generations and between the first and third ones, compared with the other low-energy observables, and the flavor mixings are induced by the neutrino Yukawa interaction. The current experimental bound of the neutron EDM may imply that the right-handed tau neutrino mass is smaller than about 10^{14} GeV in the minimal supergravity scenario, and it may be improved furthermore in future experiments, such as the deuteron EDM measurement.

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arXiv2004

Edms in SUSY GUTS

Hadronic and leptonic EDMs in SUSY GUTs are reviewed in this article.

hep-ph↗
arXiv2004

CP violation in supersymmetric seesaw models

In supersymmetric (SUSY) extensions of the seesaw mechanism the neutrino Yukawa interaction induces the flavor and CP violating sfermion mass terms via the radiative correction. In this article we review the CP violating phenomena in the SUSY seesaw models.

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arXiv2004

Hadronic EDMs induced by the strangeness and constraints on supersymmetric CP phases

We consider hadronic CP violation induced by chromoelectric dipolemoments (CEDMs) of light quarks and the QCD theta parameter ($?overline{?theta}$). We concentrate on the strange quark CEDM especially in this paper. Using effective CP violating nucleon interactions induced by the CEDMs and $?overline{?theta}$ with the SU(3) chiral Lagrangian technique, we calculate the EDMs for the $^{199}$Hg atom, neutron and deuteron. We also discuss supersymmetric contributions to the electric dipole moments with the mass insertion approximations and give stringent constraints on the CP phases of the flavor changing SUSY breaking terms.

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arXiv2004

Flavor and CP Violation Induced by Atmospheric Neutrino Mixing

Neutrino oscillation experiments suggest existence of new flavor-violating interactions in high energy scale. It may be possible to probe them by the flavor- and CP-violating processes in leptons and hadrons in the supersymmetric (SUSY) models. In this article the third-generation flavor violation is reviewed in the SUSY seesaw model and SUSY SU(5) GUT with the right-handed neutrinos.

hep-ph↗
arXiv2003

$B\to ϕK_s$ versus Electric Dipole Moment of $^{199}$Hg Atom in Supersymmetric Models with Right-handed Squark Mixing

The correlation between the CP asymmetry in $B\to ϕK_s$ ($S_{ϕK_s}$) and the chromoelectric dipole moment (CEDM) of strange quark ($d_s^C$), which is constrained by the electric dipole moment (EDM) of $^{199}$Hg, is studied in the supersymmetric (SUSY) models with the right-handed squark mixing. It is known that, if the right-handed bottom and strange squarks have a CP-violating mixing, such as in the SUSY SU(5) GUT with right-handed neutrinos, the induced gluon-penguin diagram may give a sizable contribution to $S_{ϕK_s}$. However, when the left-handed bottom and strange squarks also have a mixing, the conspiracy of the left and right-handed squarks may lead to a sizable $d_s^C$, which is enhanced by $m_b/m_s$. While the estimate for the EDM of $^{199}$Hg, induced by $d^C_s$, might have large uncertainties due to the hadron and nuclear dynamics, the current bound implies the gluon penguin contribution by the right-handed squarks to $S_{ϕK_s}$ should be suppressed and the deviation of $S_{ϕK_s}$ from the Standard Model may not be so large. Also, we discuss the constraint from the EDM of $^{199}$Hg in the SUSY SU(5) GUT with the right-handed neutrinos.

hep-ph↗
arXiv2003

Explosive Dark Matter Annihilation

If the Dark Matter (DM) in the Universe has interactions with the standard-model particle, the pair annihilation may give the imprints in the cosmic ray. In this paper we study the pair annihilation processes of the DM, which is neutral, however has the electroweak (EW) gauge non-singlet. In this estimation the non-relativistic (NR) effective theory in the EW sector is a suitable technique. We find that if the DM mass is larger than about 1 TeV, the attractive Yukawa potentials induced by the EW gauge bosons have significant effects on the DM annihilation processes, and the cross sections may be enhanced by several orders of magnitude, due to the zero energy resonance under the potentials. Especially, the annihilation to two $γ$'s might have a comparable cross section to other tree-level processes, while the cross section under the conventional calculation is suppressed by a loop factor. We also discuss future sensitivities to the $γ$ ray from the galactic center by the GLAST satellite detector and the Air Cerenkov Telescope (ACT) arrays.

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arXiv2003

A Detailed Study of the Gluino Decay into the Third Generation Squarks at the CERN LHC

In supersymmetric models a gluino can decay into tb\tildeχ^{\pm}_1 through a stop or a sbottom. The decay chain produces an edge structure in the m_{tb} distribution. Monte Carlo simulation studies show that the end point and the edge height would be measured at the CERN LHC by using a sideband subtraction technique. The stop and sbottom masses as well as their decay branching ratios are constrained by the measurement. We study interpretations of the measurement in the minimal supergravity model. We also study the gluino decay into tb and \tildeχ^{\pm}_2 as well as the influence of the stop left-right mixing on the m_{bb} distribution of the tagged $tb$ events.

hep-ph↗
arXiv2003

GUT relation in Neutrino-Induced Flavor Physics in SUSY SU(5) GUT

In the SUSY SU(5) GUT with the right-handed neutrinos, the neutrino Yukawa coupling induces the flavor-violating mass terms for the right-handed down squarks and left-handed sleptons, and they lead to imprint on the flavor physics in the hadronic and leptonic sectors. In this paper we study CP violation in $B_d^0$ and $B_s^0$, which is induced by the tau-neutrino Yukawa coupling. In particular, we notice the correlation of the CP asymmetries in $B_d^0\to ϕK_s$ ($S_{ϕK_s}$) and $B_s^0\to J/ψϕ$ ($S_{J/ψϕ}$) with other observables, such as $Br(τ\toμγ)$, the muon EDM ($d_μ$), and the mixing-induced CP asymmetry in $B_d^0\to M_s^0γ$ ($A_{bsg}$), since they have a common origin of the CP and flavor violation. The measurements are expected to play a significant role for consistency check of the SUSY SU(5) GUT. The hierarchical right-handed neutrino masses make the correlation better. We find that the current bound on $Br(τ\toμγ)$ constrains the allowed region for $S_{ϕK_s}$ in this model.

hep-ph↗
arXiv2003

Unitarity and Higher-Order Corrections in Neutralino Dark Matter Annihilation into Two Photons

The neutralino pair annihilation into two photons in our galactic halo gives a robust dark matter signal, since it would give a quasi-monotonic gamma ray. This process is radiatively-induced, and the full-one loop calculation was done previously. However, for the heavy wino-like or Higgsino-like neutralino, the one-loop cross section violates unitarity, therefore the higher-order corrections may be important. We construct a non-relativistic theory for chargino and neutralino two-body states, and estimate all-order QED corrections and two-loop corrections by $Z$ and/or $W$ exchange. We find that the critical mass, above that the two-loop contribution is larger than one-loop one, is about 8 TeV (O(10) TeV) in the limit where neutralino is wino (Higgsino)-like, respectively. Around and above the critical mass, the all-order Z and/or W exchange must be included to estimate the cross section. On the other hand, the QED corrections depend on the mass difference between the neutralino and chargino. In the wino-like limit where neutralino is highly degenerate with chargino in mass, we find that QED corrections enhance the pair annihilation cross section by 1.5-2.

hep-ph↗
arXiv2002

A New Parametrization of the Seesaw Mechanism and Applications in Supersymmetric Models

We present a new parametrization of the minimal seesaw model, expressing the heavy-singlet neutrino Dirac Yukawa couplings $(Y_ν)_{ij}$ and Majorana masses $M_{N_i}$ in terms of effective light-neutrino observables and an auxiliary Hermitian matrix $H.$ In the minimal supersymmetric version of the seesaw model, the latter can be related directly to other low-energy observables, including processes that violate charged lepton flavour and CP. This parametrization enables one to respect the stringent constraints on muon-number violation while studying the possible ranges for other observables by scanning over the allowed parameter space of the model. Conversely, if any of the lepton-flavour-violating process is observed, this measurement can be used directly to constrain $(Y_ν)_{ij}$ and $M_{N_i}.$ As applications, we study flavour-violating $τ$ decays and the electric dipole moments of leptons in the minimal supersymmetric seesaw model.

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