Masahiro Ibe 교수

We discuss the lightest Higgs boson mass in the minimal supersymmetric Standard Model with “pure gravity mediation”. By requiring that the model provides the observed dark matter density, we find that the lightest Higgs boson is predicted to be below 132 GeV. We also find that the upper limit on the lightest Higgs boson mass becomes 128 GeV, if we further assume thermal leptogenesis mechanism as the origin of baryon asymmetry of universe. The interrelations between the Higgs boson mass and the g

A bstract The elastic scattering of an atomic nucleus plays a central role in dark matter direct detection experiments. In those experiments, it is usually assumed that the atomic electrons around the nucleus of the target material immediately follow the motion of the recoil nucleus. In reality, however, it takes some time for the electrons to catch up, which results in ionization and excitation of the atoms. In previous studies, those effects are taken into account by using the so-called Migdal

We point out that annihilation of dark matter in the galactic halo can be enhanced relative to that in the early Universe due to a Breit-Wigner tail, if the dark matter annihilates through a pole just below the threshold. This provides a new explanation to the ``boost factor'' which is suggested by the recent data of the PAMELA, ATIC and PPB-BETS cosmic ray experiments.

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 gra

We discuss gauge mediation models where the doublet messengers and Higgs doublets are allowed to mix through a “charged” coupling. The charged coupling replaces messenger parity as a means of suppressing flavor changing neutral currents without introducing any unwanted CP violation. As a result of this mixing between the Higgs doublets and the messengers, relatively large A-terms are generated at the messenger scale. These large A-terms produce a distinct weak scale mass spectrum. Particularly,

The IceCube experiment has recently reported a high energy neutrino spectrum between the TeV and PeV scales. The observed neutrino flux can be as a whole well fitted by a simple power law of the neutrino energy ${E}_{\ensuremath{\nu}}$, ${E}_{\ensuremath{\nu}}^{\ensuremath{-}{\ensuremath{\gamma}}_{\ensuremath{\nu}}}$ (${\ensuremath{\gamma}}_{\ensuremath{\nu}}\ensuremath{\simeq}2$). As a notable feature of the spectrum, however, it has a gap between 500 TeV and 1 PeV. Although the existence of th

The seesaw mechanism that explains the small neutrino masses comes naturally with supersymmetric (SUSY) grand-unification and leptogenesis. However, the framework suffers from the SUSY flavor and CP problems, and has a severe cosmological gravitino problem. We propose anomaly mediation as a simple solution to all these problems, which is viable once supplemented by the $D$-terms for $U(1{)}_{Y}$ and $U(1{)}_{B\ensuremath{-}L}$. Even though the right-handed neutrino mass explicitly breaks $U(1{)}

Sommerfeld enhancement and Breit–Wigner enhancement of the dark matter annihilation have been proposed to explain the “boost factor” which is suggested by observed cosmic ray excesses. Although these two scenarios can provide almost indistinguishable effects on the cosmic ray fluxes, the cross sections of the self-interaction in those enhancement mechanisms are drastically different. As a result, we might be able to distinguish them by examining the effects of the self-interaction on the dark ma

A bstract I-balls/oscillons are long-lived and spatially localized solutions of real scalar fields. They are produced in various contexts of the early universe in, such as, the inflaton evolution and the axion evolution. However, their decay process has long been unclear. In this paper, we derive an analytic formula of the decay rate of the I-balls/oscillons within the classical field theory. In our approach, we calculate the Poynting vector of the perturbation around the I-ball/oscillon profile

One of important properties of dark matter is its stability. The U(1)B–L gauge symmetry is the most attractive symmetry to guarantee the stability. Though the symmetry is expected to be broken at very high energy scale to account for tiny neutrino masses through the seesaw mechanism, the residual discrete symmetry of U(1)B–L can stabilize the dark matter naturally. We prove that, when there is new physics connecting B–L charges of dark matter and standard model particles at the scale between the

Gravitinos and hidden sector fields often cause a cosmological disaster in supersymmetric models. We find that a model with gravitational gauge mediation solves such a problem quite naturally. The $\ensuremath{\mu}$-problem is also absent in the model. Moreover, the abundance of gravitinos explains correct amount of dark matter of the universe. The dark matter abundance can be calculated without detailed information on the thermal history of the universe such as the reheating temperature after i

A bstract Asymmetric dark matter (ADM) is an attractive framework relating the observed baryon asymmetry of the Universe to the dark matter density. A composite particle in a new strong dynamics is a promising candidate for ADM as the strong dynamics naturally explains the ADM mass in the GeV range. Its large annihilation cross section due to the strong dynamics leaves the asymmetric component to be dominant over the symmetric component. In such composite ADM scenarios, the dark sector has a rel