Kazunori Nakayama

Learn More
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(More)
We study the effects of dark matter annihilation during and after the cosmic recombination epoch on the cosmic microwave background anisotropy, taking into account the detailed energy deposition of the annihilation products. It is found that a fairly stringent constraint on the annihilation cross section is imposed for TeV scale dark matter masses from WMAP(More)
The pp → ppη reaction is investigated within a relativistic meson-exchange model of hadronic interactions. We explore the role of nucleonic and mesonic, as well as theN resonance currents, in producing η mesons. In order to learn more about the production mechanisms, new measurements in the energy region far from the threshold are required. PACS: 13.60Le,(More)
We develop a formalism to study non-Gaussianity in both curvature and isocurvature perturbations. It is shown that non-Gaussianity in the isocurvature perturbation between dark matter and photons leaves distinct signatures in the CMB temperature fluctuations, which may be confirmed in future experiments, or possibly, even in the currently available(More)
Light scalars may be ubiquitous in nature, and their quantum fluctuations can produce large non-Gaussianity in the cosmic microwave background temperature anisotropy. The non-Gaussianity may be accompanied with a small admixture of isocurvature perturbations, which often have correlations with the curvature perturbations. We present a general method to(More)
Non-Gaussianity may exist in the CDM isocurvature perturbation. We provide general expressions for the bispectrum and trispectrum of both adiabatic and isocurvature pertubations. We apply our result to the QCD axion case, and found a consistency relation between the coefficients of the bispectrum and trispectrum : τ (iso) NL ≃ 10 3[f (iso) NL ] 4/3, if the(More)
The production of ω-mesons in proton-proton collisions for proton incident energies up to 2.2 GeV is investigated within a mesonexchange model of hadronic interactions. We find a large cancellation between the dominant πρω meson-exchange current and nucleonic current contributions. A comparison with preliminary data from SATURNE calls for the inclusion of(More)
BACKGROUND Secondary hyperparathyroidism (SHPT) is one of the common complications in dialysis patients, and is associated with increased risk of vascular calcification. The effects of cinacalcet hydrochloride treatment on bone and mineral metabolism have been previously reported, but the benefit of cinacalcet on vascular calcification remains uncertain.(More)