Gravitational Wave Background and Non-Gaussianity as a Probe of the Curvaton Scenario (2009)
Nakayama, Kazunori, Yokoyama, Jun'ichi
We study observational implications of the stochastic gravitational wave background and a non-Gaussian feature of scalar perturbations on the curvaton mechanism of the generation of density/curvature...
Constraining light gravitino mass from cosmic microwave background (2009)
Ichikawa, Kazuhide, Kawasaki, Masahiro, Nakayama, Kazunori, Sekiguchi, Toyokazu, Takahashi, Tomo
We investigate the possibilities of constraining the light gravitino mass m3/2 from future cosmic microwave background (CMB) surveys. A model with light gravitino with the mass m3/2< O (10)eV is of...
Effects of Dark Matter Annihilation on the Cosmic Microwave Background (2009)
Kanzaki, Toru, Kawasaki, Masahiro, Nakayama, Kazunori
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 R-axion and non-Gaussianity (2009)
Nakayama, Kazunori, Takahashi, Fuminobu
We study cosmological implications of an R-axion, a pseudo Nambu-Goldstone boson associated with spontaneous breaking of an U(1)_R symmetry, focusing on its quantum fluctuations generated during...
Upward muon signals at neutrino detectors as a probe of dark matter properties (2009)
Hisano, Junji, Nakayama, Kazunori, Yang, Masaki J. S.
We study upward muon flux at neutrino detectors such as Super-Kamiokande resulting from high-energy neutrinos produced by the dark matter annihilation/decay at the Galactic center. In particular, we...
Constraining Light Gravitino Mass from Cosmic Microwave Background (2009)
Ichikawa, Kazuhide, Kawasaki, Masahiro, Nakayama, Kazunori, Sekiguchi, Toyokazu, Takahashi, Tomo
We investigate the possibilities of constraining the light gravitino mass m_{3/2} from future cosmic microwave background (CMB) surveys. A model with light gravitino with the mass m_{3/2}
Non-Gaussianity from Isocurvature Perturbations : Analysis of Trispectrum (2009)
Kawakami, Etsuko, Kawasaki, Masahiro, Nakayama, Kazunori, Takahashi, Fuminobu
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...
Phenomenological Aspects of Horava-Lifshitz Cosmology (2009)
Mukohyama, Shinji, Nakayama, Kazunori, Takahashi, Fuminobu, Yokoyama, Shuichiro
We show that, assuming the dispersion relation proposed recently by Horava in the context of quantum gravity, radiation energy density exhibits a peculiar dependence on the scale factor; the...
Diffuse gamma-ray background and cosmic-ray positrons from annihilating dark matter (2009)
Kawasaki, Masahiro, Kohri, Kazunori, Nakayama, Kazunori
We study the annihilating dark matter contribution to the extra-galactic diffuse gamma-ray background spectrum, motivated by the recent observations of cosmic-ray positron/electron anomalies. The...
Signatures of dark matter annihilation in the light of PAMELA/ATIC anomaly (2009)
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 discuss...
Cosmic Rays from Dark Matter Annihilation and Big-Bang Nucleosynthesis (2009)
Hisano, Junji, Kawasaki, Masahiro, Kohri, Kazunori, Moroi, Takeo, Nakayama, Kazunori
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...
Hisano, Junji, Kawasaki, Masahiro, Kohri, Kazunori, Nakayama, Kazunori
The excess of cosmic-ray electron and positron fluxes measured by the PAMELA satellite and ATIC balloon experiments may be interpreted as the signals of the dark matter annihilation or decay into...
Cosmological Moduli Problem from Thermal Effects (2008)
Nakayama, Kazunori, Takahashi, Fuminobu
We estimate the cosmological abundance of a modulus field that has dilatonic couplings to gauge fields, paying particular attention to thermal corrections on the modulus potential. We find that a...
Positron/Gamma-Ray Signatures of Dark Matter Annihilation and Big-Bang Nucleosynthesis (2008)
Hisano, Junji, Kawasaki, Masahiro, Kohri, Kazunori, Nakayama, Kazunori
The positron excess observed by the PAMELA experiment may come from dark matter annihilation, if the annihilation cross section is large enough. We show that the dark matter annihilation scenarios to...
Hilltop Non-Gaussianity (2008)
Kawasaki, Masahiro, Nakayama, Kazunori, Takahashi, Fuminobu
We study non-Gaussianity induced by a pseudo Nambu-Goldstone boson with a cosine-type scalar potential. We focus on how the non-Gaussianity is affected when the pseudo Nambu-Goldstone boson rolls...
A General Analysis of Non-Gaussianity from Isocurvature Perturbations (2008)
Kawasaki, Masahiro, Nakayama, Kazunori, Sekiguchi, Toyokazu, Suyama, Teruaki, Takahashi, Fuminobu
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...
Non-Gaussianity from Baryon Asymmetry (2008)
Kawasaki, Masahiro, Nakayama, Kazunori, Takahashi, Fuminobu
We study a scenario that large non-Gaussianity arises from the baryon asymmetry of the Universe. There are baryogenesis scenarios containing a light scalar field, which may result in baryonic...
Non-Gaussianity from isocurvature perturbations (2008)
Kawasaki, Masahiro, Nakayama, Kazunori, Sekiguchi, Toyokazu, Suyama, Teruaki, Takahashi, Fuminobu
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...
Direct/indirect detection signatures of nonthermally produced dark matter (2008)
Nagai, Minoru, Nakayama, Kazunori
We study direct and indirect detection possibilities of neutralino dark matter produced non-thermally by e.g. the decay of long-lived particles, as is easily implemented in the case of anomaly or...
Probing reheating temperature of the universe with gravitational wave background (2008)
Nakayama, Kazunori, Saito, Shun, Suwa, Yudai, Yokoyama, Jun'ichi
Thermal history of the universe after big-bang nucleosynthesis (BBN) is well understood both theoretically and observationally, and recent cosmological observations also begin to reveal the...
Space laser interferometers can determine the thermal history of the early Universe (2008)
Nakayama, Kazunori, Saito, Shun, Suwa, Yudai, Yokoyama, Jun'ichi
It is shown that space-based gravitational wave detectors such as DECIGO and/or Big Bang Observer (BBO) will provide us with invaluable information on the cosmic thermal history after inflation and...
Solving Cosmological Problems of Supersymmetric Axion Models in an Inflationary Universe (2008)
Kawasaki, Masahiro, Nakayama, Kazunori
We revisit inflationary cosmology of axion models in the light of recent developments on the inflaton decay in supergravity. We find that all the cosmological difficulties, including gravitino, axino...
Cosmological implications of supersymmetric axion models (2007)
Kawasaki, Masahiro, Nakayama, Kazunori, Senami, Masato
We derive general constraints on 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...
Nonthermal dark matter in mirage mediation (2007)
Nagai, Minoru, Nakayama, Kazunori
In mirage-mediation models there exists a modulus field whose mass is O(1000) TeV and its late-decay may significantly change the standard thermal relic scenario of the dark matter. We study...
Baryon Asymmetry in a Heavy Moduli Scenario (2007)
Kawasaki, Masahiro, Nakayama, Kazunori
In some models of supersymmetry breaking, modulus fields are heavy enough to decay before BBN. But the large entropy produced via moduli decay significantly dilutes the preexisting baryon asymmetry...
Increasing the effective number of neutrinos with decaying particles (2007)
Ichikawa, Kazuhide, Kawasaki, Masahiro, Nakayama, Kazunori, Senami, Masato, Takahashi, Fuminobu
We present models of decaying particles for increasing the effective number of neutrinos N_nu after big bang nucleosynthesis but before the structure formation begins. We point out that our scenario...
Affleck-Dine baryogenesis in anomaly-mediated SUSY breaking (2006)
Kawasaki, Masahiro, Nakayama, Kazunori
It has been known that in anomaly-mediated SUSY breaking model Affleck-Dine baryogenesis does not work due to trapping of Affleck-Dine field into charge-breaking minima. We show that when...
Late-time Affleck-Dine baryogenesis after thermal inflation (2006)
Kawasaki, Masahiro, Nakayama, Kazunori
Thermal inflation can solve serious cosmological problems such as overproduction of gravitinos and moduli. However, it also dilutes the preexisting baryon asymmetry. We investigate a possibility that...
Self-Similar Evolution of Relativistic Shock Waves Emerging from Plane-Parallel Atmospheres (2005)
Nakayama, Kazunori, Shigeyama, Toshikazu
We study the evolution of the ultra-relativistic shock wave in a plane-parallel atmosphere adjacent to a vacuum and the subsequent breakout phenomenon. When the density distribution has a power law...