Ichikawa, Kazuhide, Myoraku, Toshiyuki, Fukushima, Akinori, Ishihara, Yoshio, Isaki, Ryuichiro, Takeguchi, Toshio, ...
We investigate a reaction of boron trichloride (BCl3) with iron(III) hydroxide (Fe (OH)3) by ab initio quantum chemical calculation as a simple model for a reaction of iron impurities in BCl3 gas. We...
Neutrino mass from cosmology: Impact of high-accuracy measurement of the Hubble constant (2009)
Sekiguchi, Toyokazu, Ichikawa, Kazuhide, Takahashi, Tomo, Greenhill, Lincoln
Non-zero neutrino mass would affect the evolution of the Universe in observable ways, and a strong constraint on the mass can be achieved using combinations of cosmological data sets. We focus on the...
Ichikawa, Kazuhide, Myoraku, Toshiyuki, Fukushima, Akinori, Ishihara, Yoshio, Isaki, Ryuichiro, Takeguchi, Toshio, ...
We investigate a reaction of boron trichloride (BCl3) with iron(III) hydroxide (Fe(OH)3) by ab initio quantum chemical calculation as a simple model for a reaction of iron impurities in BCl3 gas. We...
Nakashima, Masahiro, Ichikawa, Kazuhide, Nagata, Ryo, Yokoyama, Jun'ichi
We investigate constraints on the time variation of the fine structure constant between the recombination epoch and the present epoch, $\Delta\alpha/\alpha \equiv (\alpha_{rec} -...
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...
Measuring the History of Cosmic Reionization using the 21-cm PDF from Simulations (2009)
Ichikawa, Kazuhide, Barkana, Rennan, Iliev, Ilian T., Mellema, Garrelt, Shapiro, Paul
The 21-cm PDF (i.e., distribution of pixel brightness temperatures) is expected to be highly non-Gaussian during reionization and to provide important information on the distribution of density and...
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}
Constraints on neutrino masses from WMAP5 and BBN in the lepton asymmetric universe (2009)
Shiraishi, Maresuke, Ichikawa, Kazuhide, Ichiki, Kiyotomo, Sugiyama, Naoshi, Yamaguchi, Masahide
In this paper, we put constraints on neutrino properties such as mass $m_{\nu}$ and degeneracy parameters $\xi_i$ from WMAP5 data and light element abundances by using a Markov chain Monte Carlo...
Primordial Curvature Fluctuation and Its Non-Gaussianity in Models with Modulated Reheating (2008)
Ichikawa, Kazuhide, Suyama, Teruaki, Takahashi, Tomo, Yamaguchi, Masahide
We investigate non-Gaussianity in the modulated reheating scenario where fluctuations of the decay rate of the inflaton generate adiabatic perturbations, paying particular attention to the...
Probing the Effective Number of Neutrino Species with Cosmic Microwave Background (2008)
Ichikawa, Kazuhide, Sekiguchi, Toyokazu, Takahashi, Tomo
We discuss how much we can probe the effective number of neutrino species N_nu with cosmic microwave background alone. Using the data of WMAP, ACBAR, CBI and BOOMERANG experiments, we obtain a...
Non-Gaussianity, Spectral Index and Tensor Modes in Mixed Inflaton and Curvaton Models (2008)
Ichikawa, Kazuhide, Suyama, Teruaki, Takahashi, Tomo, Yamaguchi, Masahide
We study non-Gaussianity, the spectral index of primordial scalar fluctuations and tensor modes in models where fluctuations from the inflaton and the curvaton can both contribute to the present...
Primordial Helium Abundance from CMB: a constraint from recent observations and a forecast (2007)
Ichikawa, Kazuhide, Sekiguchi, Toyokazu, Takahashi, Tomo
We studied a constraint on the primordial helium abundance Y_p from current and future observations of CMB. Using the currently available data from WMAP, ACBAR, CBI and BOOMERANG, we obtained the...
Neutrino mass constraint from CMB and its degeneracy with other cosmological parameters (2007)
We show that the cosmic microwave background (CMB) data of WMAP can give subelectronvolt limit on the neutrino mass: m_nu < 0.63 eV (95% CL). We also investigate its degeneracy with other...
The Hubble constant and dark energy from cosmological distance measures (2007)
Ichikawa, Kazuhide, Takahashi, Tomo
We study how the determination of the Hubble constant from cosmological distance measures is affected by models of dark energy and vice versa. For this purpose, constraints on the Hubble constant and...
Solving the cosmic lithium problems with primordial late-decaying particles (2007)
Cumberbatch, Daniel, Ichikawa, Kazuhide, Kawasaki, Masahiro, Kohri, Kazunori, Silk, Joseph, Starkman, Glenn D.
We investigate the modifications to predictions for the abundances of light elements from standard Big-Bang nucleosynthesis when exotic late-decaying particles with lifetimes exceeding ~1 sec are...
Cosmological Constraint on the Effective Number of Neutrino Species (2007)
We discuss constraints on the effective number of neutrino species Nnu from recent cosmological observations such as CMB, LSS, BBN, including our own analysis which uses the WMAP and the Luminous Red...
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...
Dark Energy Parametrizations and the Curvature of the Universe (2006)
Ichikawa, Kazuhide, Takahashi, Tomo
We investigate observational constraints on the curvature of the universe not restricting ourselves to a cosmological constant as dark energy, in particular allowing a dark energy equation of state...
Ichikawa, Kazuhide, Kawasaki, Masahiro, Takahashi, Fuminobu
We derive constraint on the effective number of neutrino species N_nu from the cosmic microwave background power spectrum of the WMAP and galaxy clustering power spectrum of the SDSS luminous red...
Implications of cosmic strings with time-varying tension on CMB and large scale structure (2006)
Ichikawa, Kazuhide, Takahashi, Tomo, Yamaguchi, Masahide
We investigate cosmological evolution and implications of cosmic strings with time-dependent tension. We derive basic equations of time development of the correlation length and the velocity of such...
Ichikawa, Kazuhide, Kawasaki, Masahiro, Sekiguchi, Toyokazu, Takahashi, Tomo
We investigate how the nature of dark energy affects the determination of the curvature of the universe from recent observations. For this purpose, we consider the constraints on the matter and dark...
Limit on the Neutrino Mass from the WMAP Three Year Data (2006)
Fukugita, Masataka, Ichikawa, Kazuhide, Kawasaki, Masahiro, Lahav, Ofer
We derive an upper limit on the neutrino mass from the WMAP three-year data alone by employing a deterministic minimisation method based on a grid search in multi-parameter space. Assuming the flat...
CMB constraints on the fine structure constant (2006)
Ichikawa, Kazuhide, Kanzaki, Toru, Kawasaki, Masahiro
We study constraints on time variation of the fine structure constant alpha from cosmic microwave background (CMB) taking into account simultaneous change in alpha and the electron mass m_e which...
Revisiting the Constraint on the Helium Abundance from CMB (2006)
Ichikawa, Kazuhide, Takahashi, Tomo
We revisit the constraint on the primordial helium mass fraction Yp from observations of cosmic microwave background (CMB) alone. By minimizing chi square of recent CMB experiments over 6 other...
Dark Energy Evolution and the Curvature of the Universe from Recent Observations (2005)
Ichikawa, Kazuhide, Takahashi, Tomo
We discuss the constraints on the time-varying equation of state for dark energy and the curvature of the universe using observations of type Ia supernovae from Riess et al. and the most recent...
Ichikawa, Kazuhide, Takahashi, Tomo
We discuss the possibilities of the simultaneous determination of the neutrino masses and the evolution of dark energy from future cosmological observations such as cosmic microwave background (CMB),...
Ichikawa, Kazuhide, Kawasaki, Masahiro, Takahashi, Fuminobu
We study how the oscillations of the neutrinos affect their thermalization process during the reheating period with temperature O(1) MeV in the early universe. We follow the evolution of the neutrino...
Constraining Neutrino Masses by CMB Experiments Alone (2004)
Ichikawa, Kazuhide, Fukugita, Masataka, Kawasaki, Masahiro
It is shown that a subelectronvolt upper limit can be derived on the neutrino mass from the CMB data alone in the Lambda CDM model with the power-law adiabatic perturbations, without the aid of any...
Solving the discrepancy among the light elements abundances and WMAP (2004)
Ichikawa, Kazuhide, Kawasaki, Masahiro, Takahashi, Fuminobu
Within the standard big bang nucleosynthesis (BBN) and cosmic microwave background (CMB) framework, the baryon density measured by the Wilkinson Microwave Anisotropy Probe (WMAP) or the primordial D...
Ichikawa, Kazuhide, Kawasaki, Masahiro
We calculate primordial abundances of light elements produced during big bang nucleosynthesis when the fine structure constant and/or the cosmic expansion rate take non-standard values. We compare...
Cosmology and two-body problem of D-branes (2003)
Takahashi, Keitaro, Ichikawa, Kazuhide
In this paper, we investigate the dynamics and the evolution of the scale factor of a probe Dp-brane which move in the background of source Dp-branes. Action of the probe brane is described by the...
Comments on the Evolution of Strongly Degenerate Neutrinos in the Early Universe (2003)
Ichikawa, Kazuhide, Kawasaki, Masahiro
We reconsider the evolution of strongly degenerate neutrinos in the early universe. Our chief concern is the validity of the entropy conservation after the neutrino annihilation process has frozen...
Remarks on the Cosmic Density of Degenerate Neutrinos (2002)
Ichikawa, Kazuhide, Kawasaki, M.
We re-investigate the evolution of the strongly degenerate neutrinos in the early universe. With the larger degeneracy, the neutrino number freezes at higher temperatures because the neutrino...
Constraining the variation of the coupling constants with big bang nucleosynthesis (2002)
Ichikawa, Kazuhide, Kawasaki, M.
We consider the possibility of the coupling constants of the $SU(3)\times SU(2)\times U(1)$ gauge interactions at the time of big bang nucleosynthesis having taken different values from what we...