研究者詳細 - 杉山　直

論文 - 杉山　直

分割表示 94 件中 61 - 80 件目／全件表示 >>

Systematic study of gravitational waves from galaxy mergers 査読有り

Takahiro Inagaki, Keitaro Takahashi, Shogo Masaki, Naoshi Sugiyama

Physical Review D 82 巻 ( 12 ) 頁： 124007 2010年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

A systematic study of gravitational waves from galaxy mergers, through N-body simulations, was performed. In particular, we investigated the relative importance of galaxy components (disk, bulge and halo) and effects of initial relative velocity, relative angular momentum and mass ratio of the galaxies. We found that the features of light curve of gravitational waves, such as peak width and luminosity, are reliably simulated with particle numbers larger than ˜104. Dominant contribution to gravitational wave emission came from the halo component, while peak luminosity amounted to 1031erg/sec for the collision of two halos with mass 3.8×1012h-1Mȯ. We also found that the initial relative velocity in the direction of the initial separation did not significantly affect gravitational wave emission, while the initial relative angular momentum broadened the peak width and suppressed the luminosity. Mass dependence of the peak luminosity was also investigated, and we obtained evidence that the luminosity is proportional to the cubic mass when the scaling relation is satisfied. This behavior was considered by a simple analysis.

Ghost dark matter 査読有り

Tomonori Furukawa, Shuichiro Yokoyama, Kiyotomo Ichiki, Naoshi Sugiyama, Shinji Mukohyama

Journal of Cosmology and Astroparticle Physics 2010 巻 ( 05 ) 頁： 007 2010年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

We revisit ghost dark matter, the possibility that ghost condensation may serve as an alternative to dark matter. In particular, we investigate the Friedmann-Robertson-Walker (FRW) background evolution and the large-scale structure (LSS) in the ΛGDM universe, i.e. a late-time universe dominated by a cosmological constant and ghost dark matter. The FRW background of the ΛGDM universe is indistinguishable from that of the standard ΛCDM universe if Mgtrsim1eV, where M is the scale of spontaneous Lorentz breaking. From the LSS we find a stronger bound: Mgtrsim10eV. For smaller M, ghost dark matter would have non-negligible sound speed after the matter-radiation equality, and thus the matter power spectrum would significantly differ from observation. These bounds are compatible with the phenomenological upper bound M<100GeV known in the literature.

DECIGO and DECIGo pathfinder 査読有り

Masaki Ando, Seiji kawamura, et al.

Classical and Quantum Gravity 27 巻 ( 8 ) 頁： 084010 2010年4月

記述言語：英語掲載種別：研究論文（学術雑誌）

A space gravitational-wave antenna, DECIGO (DECI-hertz interferometer Gravitational wave Observatory), will provide fruitful insights into the universe, particularly on the formation mechanism of supermassive black holes, dark energy and the inflation of the universe. In the current pre-conceptual design, DECIGO will be comprising four interferometer units; each interferometer unit will be formed by three drag-free spacecraft with 1000 km separation. Since DECIGO will be an extremely challenging mission with high-precision formation flight with long baseline, it is important to increase the technical feasibility before its planned launch in 2027. Thus, we are planning to launch two milestone missions. DECIGO pathfinder (DPF) is the first milestone mission, and key components for DPF are being tested on ground and in orbit. In this paper, we review the conceptual design and current status of DECIGO and DPF.

Forecast constraints on inflation from combined CMB and gravitational wave direct detection experiments 査読有り

Sachiko Kuroyanagi, Christopher Gordon, Joseph Silk, Naoshi Sugiyama

Physical Review D 81 巻 ( 8 ) 頁： 083524 2010年4月

記述言語：英語掲載種別：研究論文（学術雑誌）

We study how direct detection of the inflationary gravitational wave background constrains inflationary parameters and complements CMB polarization measurements. The error ellipsoids calculated using the Fisher information matrix approach with Planck and the direct detection experiment, Big Bang Observer (BBO), show different directions of parameter degeneracy, and the degeneracy is broken when they are combined. For a slow-roll parametrization, we show that BBO could significantly improve the constraints on the tensor-to-scalar ratio compared with Planck alone. We also look at a quadratic and a natural inflation model. In both cases, if the temperature of reheating is also treated as a free parameter, then the addition of BBO can significantly improve the error bars. In the case of natural inflation, we find that the addition of BBO could even partially improve the error bars of a cosmic variance-limited CMB experiment.

Numerical study of primordial magnetic field amplification by inflation-produced gravitational waves 査読有り

Sachiko Kuroyanagi, Hiroyuki Tashiro, Naoshi Sugiyama

Physical Review D 81 巻 ( 2 ) 頁： 023510 2010年1月

記述言語：英語掲載種別：研究論文（学術雑誌）

We numerically study the interaction of inflation-produced magnetic fields with gravitational waves, both of which originate from quantum fluctuations during inflation. The resonance between the magnetic field perturbations and the gravitational waves has been suggested as a possible mechanism for magnetic field amplification. However, some analytical studies suggest that the effect of the inflationary gravitational waves is too small to provide significant amplification. Our numerical study shows more clearly how the interaction affects the magnetic fields and confirms the weakness of the influence of the gravitational waves. We present an investigation based on the magnetohydrodynamic approximation and take into account the differences of the Alfven speed.

Simulations of Wide-Field Weak Lensing Surveys. I. Basic Statistics and Non-Gaussian Effects 査読有り

Masanori Sato, Takashi Hamana, Ryuichi takahashi, Masahiro Takada, Naoki Yoshida, Takahiko Matsubara, Naoshi Sugiyama

The Astrophysical Journal, Volume 701 巻 ( 2 ) 頁： 945-954 2009年8月

記述言語：英語掲載種別：研究論文（学術雑誌）

We study the lensing convergence power spectrum and its covariance for a standard ΛCDM cosmology. We run 400 cosmological N-body simulations and use the outputs to perform a total of 1000 independent ray-tracing simulations. We compare the simulation results with analytic model predictions. The semianalytic model based on Smith et al. fitting formula underestimates the convergence power by ~ 30% at arcmin angular scales. For the convergence power spectrum covariance, the halo model reproduces the simulation results remarkably well over a wide range of angular scales and source redshifts. The dominant contribution at small angular scales comes from the sample variance due to the number fluctuations of halos in a finite survey volume. The signal-to-noise ratio for the convergence power spectrum is degraded by the non-Gaussian covariances by up to a factor of 5 for a weak lensing survey to zs ~ 1. The probability distribution of the convergence power spectrum estimators, among the realizations, is well approximated by a χ2 distribution with broadened variance given by the non-Gaussian covariance, but has a larger positive tail. The skewness and kurtosis have non-negligible values especially for a shallow survey. We argue that a prior knowledge on the full distribution may be needed to obtain an unbiased estimate on the ensemble-averaged band power at each angular scale from a finite volume survey.

Simulations of Baryon Acoustic Oscillations. II. Covariance Matrix of the Matter Power Spectrum 査読有り

Ryuichi Takahashi, Naoki Yoshida, Masahiro Takada, Takahiko Matsubara, Naoshi Sugiyama, Issha Kayo, Atsushi J. Nishizawa, Takahiro Nishimichi, Shun Saito, Atsushi Taruya

The Astrophysical Journal 700 巻 ( 1 ) 頁： 479-490 2009年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

We use 5000 cosmological N-body simulations of 1 h -3 Gpc3 box for the concordance ΛCDM model in order to study the sampling variances of a nonlinear matter power spectrum. We show that the non-Gaussian errors can be important even on large length scales relevant for baryon acoustic oscillations (BAOs). Our findings are the following: (1) the non-Gaussian errors degrade the cumulative signal-to-noise ratios (S/Ns) for the power spectrum amplitude by up to a factor of 2 and 4 for redshifts z = 1 and 0, respectively; (2) there is little information on the power spectrum amplitudes in the quasi-nonlinear regime, confirming the previous results; (3) the distribution of power spectrum estimators at BAO scales, among the realizations, is well approximated by a Gaussian distribution with variance that is given by the diagonal covariance component. (4) For the redshift-space power spectrum, the degradation in S/N by non-Gaussian errors is mitigated due to nonlinear redshift distortions; (5) for an actual galaxy survey, the additional shot noise contamination compromises the cosmological information inherent in the galaxy power spectrum, but also mitigates the impact of non-Gaussian errors. The S/N is degraded by up to 30% for a Wide-Field Fiber-Fed Optical Multi-Object Spectrograph-type survey; (6) the finite survey volume causes additional non-Gaussian errors via the correlations of long-wavelength fluctuations with the fluctuations we want to measure, further degrading the S/N values by about 30% even at high redshift z = 3.

Constraints on neutrino masses from WMAP5 and BBN in the lepton asymmetric universe 査読有り

Maresuke Shiraishi, Kazuhide Ichikawa, Kiyotomo Ichiki, Naoshi Sugiyama, Masahidee Yamaguchi

Journal of Cosmology and Astroparticle Physics 07 巻頁： 005 2009年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

In this paper, we put constraints on neutrino properties such as mass mν and degeneracy parameters ξi from WMAP5 data and light element abundances by using a Markov chain Monte Carlo (MCMC) approach. In order to take consistently into account the effects of the degeneracy parameters, we run the Big Bang Nucleosynthesis code for each value of ξi and the other cosmological parameters to estimate the Helium abundance, which is then used to calculate CMB anisotropy spectra instead of treating it as a free parameter. We find that the constraint on mν is fairly robust and does not vary very much even if the lepton asymmetry is allowed, and is given by ∑mν < 1.3 eV (95%C.L.).

DECIGO pathfinder 査読有り

Ando, Masaki; Kawamura, Seiji; Sato, Shuichi; Nakamura, Takashi; Tsubono, Kimio; Araya, Akito; Funaki, Ikkoh; Ioka, Kunihito; Kanda, Nobuyuki; Moriwaki, Shigenori; Musha, Mitsuru; Nakazawa, Kazuhiro; Numata, Kenji; Sakai, Shin-ichiro; Seto, Naoki; Takashima, Takeshi; Tanaka, Takahiro; Agatsuma, Kazuhiro; Aoyanagi, Koh-suke; Arai, Koji; Asada, Hideki; Aso, Yoichi; Chiba, Takeshi; Ebisuzaki, Toshikazu; Ejiri, Yumiko; Enoki, Motohiro; Eriguchi, Yoshiharu; Fujimoto, Masa-Katsu; Fujita, Ryuichi; Fukushima, Mitsuhiro; Futamase, Toshifumi; Ganzu, Katsuhiko; Harada, Tomohiro; Hashimoto, Tatsuaki; Hayama, Kazuhiro; Hikida, Wataru; Himemoto, Yoshiaki; Hirabayashi, Hisashi; Hiramatsu, Takashi; Hong, Feng-Lei; Horisawa, Hideyuki; Hosokawa, Mizuhiko; Ichiki, Kiyotomo; Ikegami, Takeshi; Inoue, Kaiki T.; Ishidoshiro, Koji; Ishihara, Hideki; Ishikawa, Takehiko; Ishizaki, Hideharu; Ito, Hiroyuki; Itoh, Yousuke; Kawashima, Nobuki; Kawazoe, Fumiko; Kishimoto, Naoko; Kiuchi, Kenta; Kobayashi, Shiho; Kohri, Kazunori; Koizumi, Hiroyuki; Kojima, Yasufumi; Kokeyama, Keiko; Wataru@Kokuyama; Kotake, Kei; Kozai, Yoshihide; Kudoh, Hideaki; Kunimori, Hiroo; Kuninaka, Hitoshi; Kuroda, Kazuaki; Maeda, Kei-ichi; Matsuhara, Hideo; Mino, Yasushi; Miyakawa, Osamu; Miyoki, Shinji; Morimoto, Mutsuko Y.; Morioka, Tomoko; Morisawa, Toshiyuki; Mukohyama, Shinji; Nagano, Shigeo; Naito, Isao; Nakamura, Kouji; Nakano, Hiroyuki; Nakao, Kenichi; Nakasuka, Shinichi; Nakayama, Yoshinori; Nishida, Erina; Nishiyama, Kazutaka; Nishizawa, Atsushi; Niwa, Yoshito; Noumi, Taiga; Obuchi, Yoshiyuki; Ohashi, Masatake; Ohishi, Naoko; Ohkawa, Masashi; Okada, Norio; Onozato, Kouji; Oohara, Kenichi; Sago, Norichika; Saijo, Motoyuki; Sakagami, Masaaki; Sakata, Shihori; Sasaki, Misao; Sato, Takashi; Shibata, Masaru; Shinkai, Hisaaki; Somiya, Kentaro; Sotani, Hajime; Sugiyama, Naoshi; Suwa, Yudai; Suzuki, Rieko; Tagoshi, Hideyuki; Takahashi, Fuminobu; Takahashi, Kakeru; Takahashi, Keitaro; Takahashi, Ryutaro; Takahashi, Ryuichi; Takahashi, Tadayuki; Takahashi, Hirotaka; Akiteru, Takamori; Takano, Tadashi; Taniguchi, Keisuke; Taruya, Atsushi; Tashiro, Hiroyuki; Torii, Yasuo; Toyoshima, Morio; Tsujikawa, Shinji; Tsunesada, Yoshiki; Ueda, Akitoshi; Ueda, Ken-ichi; Utashima, Masayoshi; Wakabayashi, Yaka; Yamakawa, Hiroshi; Yamamoto, Kazuhiro; Yamazaki, Toshitaka; Yokoyama, Jun'ichi; Yoo, Chul-Moon; Yoshida, Shijun; Yoshino, Taizoh

Classical and Quantum Gravity 26 巻 ( 9 ) 頁： 094019 2009年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

DECIGO pathfinder (DPF) is a milestone satellite mission for DECIGO (DECi-hertz Interferometer Gravitational wave Observatory), which is a future space gravitational wave antenna. DECIGO is expected to provide fruitful insights into the universe, particularly about dark energy, the formation mechanism of supermassive black holes and the inflation of the universe. Since DECIGO will be an extremely challenging mission, which will be formed by three drag-free spacecraft with 1000 km separation, it is important to increase the technical feasibility of DECIGO before its planned launch in 2024. Thus, we are planning to launch two milestone missions: DPF and pre-DECIGO. In this paper, we review the conceptual design and current status of the first milestone mission, DPF.

The 21-cm signature of early relic HII regions 査読有り

Midori Tokutani, Naoki Yoshida, S. Peng Oh, Naoshi Sugiyama

Monthly Notices of the Royal Astronomical Society 395 巻 ( 2 ) 頁： 777-780 2009年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

We calculate the spin temperature and 21-cm brightness of early HII regions around the first stars. We use outputs from cosmological radiation-hydrodynamics simulations of the formation and evolution of early HII regions. In the pre-re-ionization era, HII regions around massive primordial stars have diameters of a few kpc. The gas within the HII regions is almost fully ionized, but begins recombining after the central stars die off. The relic HII regions are then seen as bright emission sources in hydrogen 21 cm. We make brightness temperature maps of the HII regions, accounting for radiative coupling with Lyman α photons in a simplified manner. The spin temperature in the relic HII region is close to the gas kinetic temperature, generally several hundred to several thousand degrees. We show that the relic HII region can be as bright as δTb ~ 100mK in differential temperature against the cosmic microwave background for an angular resolution of subarcseconds. While individual early HII patches will not be identified by currently planned radio telescopes, the collective fluctuations from early HII regions might imprint signatures in the 21-cm background.

The Sunyaev-Zel'dovich effect and Faraday rotation contributions of galaxy groups to the CMB angular power spectrum 査読有り

Hiroyuki Tashiro, Joseph Silk, Mathieu Langer, Naoshi Sugiyama

Monthly Notices of the Royal Astronomical Society 392 巻 ( 4 ) 頁： 1421-1428 2009年2月

Modeling Nonlinear Evolution of Baryon Acoustic Oscillations: Convergence Regime of N-body Simulations and Analytic Models 査読有り

Publications of the Astronomical Society of Japan 61 巻 ( 2 ) 頁： 321-332 2009年2月

記述言語：英語掲載種別：研究論文（学術雑誌）

We used a series of cosmological N-body simulations and various analytic models to study the evolution of the matter power spectrum in real space in a Λ cold dark matter universe. We compared the results of N-body simulations against three analytical model predictions; standard perturbation theory, renormalized perturbation theory, and a closure approximation. We included the effects from a finite simulation box size under comparison. We determined the values of the maximum wavenumbers, klim1% and klim3%, below which the analytic models and the simulation results agree with accuracy to within 1 and 3 percent. We then provided a simple empirical function that describes the convergence regime determined by comparisons between our simulations and the analytical models. We found that if we use the Fourier modes within the convergence regime alone, the characteristic scale of baryon acoustic oscillations can be determined with an accuracy of 1% from future surveys with a volume of a few h-3Gpc3 at z ∼ 1 or z ∼ 3 in the absence of any systematic distortion of the power spectrum.

Optimal location of two laser-interferometric detectors for gravitational wave backgrounds at 100 MHz 査読有り

Classical and Quantum Gravity 25 巻 ( 22 ) 頁： 225011 2008年11月

Simulations of baryon acoustic oscillations - I. Growth of large-scale density fluctuations 査読有り

Ryuichi Takahashi, Naoki Yoshida, Takahiko Matsubara, Naoshi Sugiyama, Issha Kayo, Takahiro Nishimichi, Akihito Shirata, Atsushi Taruya, Shun Saito, Kazuhiro Yahata, Yasushi Suto

Monthly Notices of the Royal Astronomical Society 389 巻 ( 4 ) 頁： 1675-1682 2008年10月

Search for a Stochastic Background of 100-MHz gravitational Waves with Laser Interferometers 査読有り

Tomotada Akutsu, Seiji Kawamura, Atsushi Nishizawa, Koji Arai, Kazuhiro Yamamoto, Daisuke Tatsumi, Shigeo Nagano, Erina Nishida, Takeshi Chiba, Ryuichi Takahashi, Naoshi Sugiyama, Titsuhiro Fukushima, Toshitaka Yamazaki, Masa-Katsu Fujimoto

Physical Review Letters 101 巻 ( 10 ) 頁： 101101 2008年9月

Constraints on primordial black holes by distortions of the cosmic microwave background 査読有り

Hiroyuki Tashiro, Naoshi Sugiyama

Physical Review D 78 巻 ( 2 ) 頁： 023004 2008年7月

Electromagnetic properties of the early universe 査読有り

Keitaro Takahashi, Kiyotomo ichiki, Naoshi Sugiyama

Physical Review D 77 巻 ( 12 ) 頁： 124028 2008年6月

Cosmic Microwave Background-Weak Lensing Correlation: Analytical and Numerical Study of Nonlinearity and Implications for Dark Energy 査読有り

Atsushi Nishizawa, Eiichiro Komatsu, Naoki Yoshida, Ryuichi Takahashi, Naoshi Sugiyama

The Astrophysical Journal Letters 676 巻 ( 2 ) 頁： L93-L96 2008年4月

Analyzing WMAP Observation by Quantum Gravity 査読有り

119 巻 ( 2 ) 頁： 253-262 2008年2月

Laser-interferometric detectors for gravitational wave backgrounds at 100MHz: Detector design and sensitivity 査読有り

Atsushi Nishizawa, Seiji Kawamura, Tomotada Akutsu, Koji Arai, Kazuhiro Yamamoto, Daisuke Tatsumi, Erina Nishida, Masa-Aki Sakagami, Takeshi Chiba, Ryuichi Takahashi, Naoshi Sugiyama

77 巻 ( 2 ) 頁： 022002 2008年1月

　前のページ - 次のページ　

<杉山 直>

論文 - 杉山 直

<杉山　直>

論文 - 杉山　直