Shigeki Matsumoto

Explosive dark matter annihilation.

In this Letter we study pair annihilation processes of dark matter (DM) in the Universe, in the case that the DM is an electroweak gauge nonsinglet. In the current Universe, in which the DM is highly nonrelativistic, the nonperturbative effect may enhance the DM annihilation cross sections, especially for that to two photons, by several orders of magnitude. We also discuss sensitivities in future searches for anomalous gamma rays from the galactic center, which originate from DM annihilation.

Pure Gravity Mediation with m_{3/2} = 10-100TeV

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 tens to hundreds TeV range while the gauginos are in the hundreds GeV to TeV range. In this paper, we discuss detalis of the gaugino mass spectrum in the pure gravity mediation model. We also discuss the signals of the model at the 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.

Neutrinos at IceCube from Heavy Decaying Dark Matter

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.

Mass Splitting between Charged and Neutral Winos at Two-Loop Level

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 10–30% longer lifetime of the charged wino, with which the current constraint on the wino mass by the ATLAS experiment is improved by about 10%.

Pure gravity mediation of supersymmetry breaking at the Large Hadron Collider

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.

Direct detection of the Wino and Higgsino-like neutralino dark matter at one-loop level

The neutralino-nucleon ({chi}-tilde{sup 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 winolike and Higgsino-like LSP cases. The neutralino-nucleon scattering mediated by the Higgs {chi}-tilde{sup 0}{chi}-tilde{sup 0} and Z{chi}-tilde{sup 0}{chi}-tilde{sup 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 {sigma}{sub {chi}}{sub -tilde{sup 0}}{sub N}{approx}10{sup -45} cm{sup 2} or less.

Significant effects of second Kaluza-Klein particles on dark matter physics

We point out that Kaluza-Klein (KK) dark matter physics is drastically affected by second KK particles. In this work various interesting phenomena caused by the second KK modes are discussed. In particular, we reevaluate the annihilation cross section relevant to the thermal relic density of KK dark matter in universal extra dimension models. In these models, the first KK mode of a

Wino dark matter and future dSph observations

B

Search for the Top Partner at the LHC using Multi-b-Jet Channels

boson is a viable dark matter candidate by virtue of KK parity. We demonstrate that the KK dark matter annihilation cross section can be enhanced, compared with the tree-level cross section mediated only by first KK particles. The mass of the first KK mode of the

WIMP Dark Matter in a Well-Tempered Regime: A case study on Singlet-Doublets Fermionic WIMP

B