Masato Senami

Non-perturbative effect on thermal relic abundance of dark matter

Abstract 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 .

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 nonperturbation 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.

Cosmological implications of supersymmetric axion models

We derive general constraints on the supersymmetric extension of axion models, in particular paying careful attention to the cosmological effects of saxion. It is found that, for every mass range of the saxion from keV to TeV, severe constraints on the energy density of the saxion are imposed. Together with constraints from axino we obtain stringent upper bounds on the reheating temperature.

Increasing the effective number of neutrinos with decaying particles

We present models of decaying particles for increasing the effective number of neutrinos Nν after big bang nucleosynthesis but before the structure formation begins. We point out that our scenario not only solves the discrepancy between the constraints on Nν from these two epochs, but also provides a possible answer to deeper inconsistency in the estimation of the matter power spectrum amplitude at small scales, represented by σ8, between the WMAP and some small scale matter power measurements such as the Lyman-α forest and weak lensing. We consider (a) saxion decay into two axions; (b) gravitino decay into axino and axion; (c) Dirac right-handed sneutrino decay into gravitino and right-handed neutrino.

Relic abundance of dark matter in the minimal universal extra dimension model

We investigate the relic abundance of dark matter in the minimal universal extra dimension model including resonance processes by second Kaluza-Klein (KK) particles in all coannihilation processes. After including second KK resonance processes, the relic abundance of dark matter is reduced by about 30%. Thus, the compactification scale 1/R of the extra dimension consistent with the WMAP observation is increased by a few hundred GeV. As a result, the cosmologically allowed compactification scale is 600 GeV < 1/R < 1400 GeV for Lambda R = 20.

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

Relic abundance of LKP dark matter in UED model including effects of second KK resonances

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Role of an Aluminum Atom on Graphene for Hydrogen Adsorption

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

Productions of second Kaluza-Klein gauge bosons in the minimal universal extra dimension model at LHC

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Theoretical study of adsorption of lithium atom on carbon nanotube

boson consistent with the Wilkinson Microwave Anisotropy Probe observation is increased.