Generation of Curvature Perturbations with Extra Anisotropic Stress (2009)
Kojima, Kazuhiko, Kajino, Toshitaka, Mathews, Grant J.
We study the evolution of curvature perturbations and the cosmic microwave background (CMB) power spectrum in the presence of an hypothesized extra anisotropic stress in the early universe. Such...
Effect of Long-lived Strongly Interacting Relic Particles on Big Bang Nucleosynthesis (2009)
Kusakabe, Motohiko, Kajino, Toshitaka, Yoshida, Takashi, Mathews, Grant J.
It has been suggested that relic long-lived strongly interacting massive particles (SIMPs, or $X$ particles) existed in the early universe. We study effects of such long-lived unstable SIMPs on big...
Hayakawa, Takehito, Iwamoto, Nobuyuki, Kajino, Toshitaka, Shizuma, Toshiyuki, Umeda, Hideyuki, Nomoto, Ken'ichi
Analyzing the solar system abundances, we have found two empirical abundance scaling laws concerning the p- and s-nuclei with the same atomic number. The first scaling is s/p ratios are almost...
138La-138Ce-136Ce nuclear cosmochronometer of supernova neutrino process (2009)
Hayakawa, Takehito, Shizuma, Toshiyuki, Kajino, Toshitaka, Ogawa, Kengo, Nakada, Hitoshi
The 138La (T1/2=102 Gyr) - 138Ce - 136Ce system is proposed to be used as a nuclear cosmochronometer for measuring the time elapsed from a supernova neutrino process. This chronometer is applied to...
Constraints on the Primordial Magnetic Field from $\sigma_8$ (2008)
Yamazaki, Dai G., Ichiki, Kiyotomo, Kajino, Toshitaka, Mathews, Grant. J.
A primordial magnetic field (PMF) can affect the evolution of density field fluctuations in the early universe.In this paper we constrain the PMF amplitude $B_\lambda$ and power spectral index...
Kusakabe, Motohiko, Kajino, Toshitaka, Yoshida, Takashi, Shima, Tatsushi, Nagai, Yasuki, Kii, Toshiteru
A recent measurement of $^4$He photodisintegration reactions, $^4$He($\gamma$,$p$)$^3$H and $^4$He($\gamma$,$n$)$^3$He with laser-Compton photons shows smaller cross sections than those estimated by...
Kojima, Kazuhiko, Ichiki, Kiyotomo, Yamazaki, Dai G., Kajino, Toshitaka, Mathews, Grant J.
If a primordial magnetic field (PMF) is present during photon decoupling and afterward, a finite neutrino mass can affect all modes of the CMB. In this work, we expand on earlier studies of the...
Effects of a Primordial Magnetic Field on Low and High Multipoles of the CMB (2008)
Yamazaki, Dai G., Ichiki, Kiyotomo, Kajino, Toshitaka, Mathews, Grant J.
The existence of a primordial magnetic field (PMF) would affect both the temperature and polarization anisotropies of the cosmic microwave background (CMB). It also provides a plausible explanation...
Kusakabe, Motohiko, Kajino, Toshitaka, Boyd, Richard N., Yoshida, Takashi, Mathews, Grant J.
The $^6$Li abundance observed in metal poor halo stars exhibits a plateau similar to that for $^7$Li suggesting a primordial origin. However, the observed abundance of $^6$Li is a factor of $10^3$...
The X^- Solution to the ^6Li and ^7Li Big Bang Nucleosynthesis Problems (2007)
Kusakabe, Motohiko, Kajino, Toshitaka, Boyd, Richard N., Yoshida, Takashi, Mathews, Grant J.
The $^6$Li abundance observed in metal poor halo stars appears to exhibit a plateau as a function of metallicity similar to that for $^7$Li, suggesting a big bang origin. However, the inferred...
THE ASTROPHYSICAL JOURNAL, 561 346363, 2001 November 1 V (2007)
The American Astronomical, Wako Aoki, Sean G. Ryan, John E. Norris, Timothy C. Beers, Hiroyasu Ando, ...
We report abundance estimates for neutron capture elements, including lead (Pb), and nucleosynthesis models for their origin, in two carbon-rich, very metal-poor stars, LP 625-44 and LP 706-7. These...
Yamazaki, Dai G., Ichiki, Kiyotomo, Kajino, Toshitaka, Mathews, Grant J.
The primordial magnetic field (PMF) can strongly affect the cosmic microwave background (CMB) power spectrum and the formation of large scale structure. In this presentation, we calculate the CMB...
Neutrino Nucleus Reactions based on New Shell Model Hamiltonians (2006)
Suzuki, Toshio, Chiba, Satoshi, Yoshida, Takashi, Kajino, Toshitaka, Otsuka, Takaharu
A new shell model Hamiltonian for p-shell nuclei which properly takes into account important roles of spin-isospin interactions is used to obtain cross sections of neutrino-^12C reactions induced by...
$^6$Li Production by the Radiative Decay of Long-Lived Particles (2006)
Kusakabe, Motohiko, Kajino, Toshitaka, Mathews, Grant J.
Recent spectroscopic observations of metal poor stars have indicated that both $^7$Li and $^6$Li have abundance plateaus with respect to the metallicity. Abundances of $^7$Li are about a factor three...
Neutron-capture elements in the metal-poor globular cluster M15 (2006)
Otsuki, Kaori, Honda, Satoshi, Aoki, Wako, Kajino, Toshitaka, Mathews, Grant J.
We report on observations of six giants in the globular cluster M15 (NGC 7078) using the Subaru Telescope to measure neutron-capture elemental abundances. Our abundance analyses based on high-quality...
Yoshida, Takashi, Kajino, Toshitaka, Hartmann, Dieter H.
We constrain energy spectra of supernova neutrinos through the avoidance of an overproduction of the 11B abundance during Galactic chemical evolution. In supernova nucleosynthesis calculations with a...
Aoki, Wako, Honda, Satoshi, Beers, Timothy C., Kajino, Toshitaka, Ando, Hiroyasu, Norris, John E., ...
Elemental abundance measurements have been obtained for a sample of 18 very metal-poor stars using spectra obtained with the Subaru Telescope High Dispersion Spectrograph. Seventeen stars, among...
Nucleosynthetic signatures of the first stars (2005)
Frebel, Anna, Aoki, Wako, Christlieb, Norbert, Ando, Hiroyasu, Asplund, Martin, Barklem, Paul S., ...
The chemically most primitive stars provide constraints on the nature of the first stellar objects that formed in the Universe; elements other than hydrogen, helium and traces of lithium within these...
Yoshida, Takashi, Kajino, Toshitaka
In order to resolve the overproduction problem of 11B in supernova explosions during Galactic chemical evolution, the dependence of the ejected masses of the light elements produced through the...
Aoki, Wako, Ryan, Sean G., Iwamoto, Nobuyuki, Beers, Timothy C., Norris, John E., Ando, Hiroyasu, ...
We report on the first measurement of the Eu isotope fractions (151Eu and 153Eu) in s-process-element-enhanced, metal-poor stars. We use these ratios to investigate the 151Sm branching of s-process...
r-Process Abundance Universality and Actinide Cosmochronology (2002)
Otsuki, Kaori, Mathews, Grant J., Kajino, Toshitaka
We review recent observational and theoretical results concerning the presence of actinide nuclei on the surfaces of old halo stars and their use as an age determinant. We present model calculations...
Rapid rotation of ultra-li-depleted halo stars and their association with blue stragglers (2002)
Ryan, Sean G., Gregory, Scott G., Kolb, Ulrich, Beers, Timothy C., Kajino, Toshitaka
Observations of 18 halo main-sequence turnoff stars, four of which are extremely deficient in Li, show that three of the Li-poor ones have substantial line broadening. We attribute this to stellar...
Cosmological Nucleosynthesis in the Big-Bang and Supernovae (2002)
Recent observation of the power spectrum of Cosmic Microwave Background (CMB) Radiation has exhibited that the flat cosmology is most likely. This suggests too large universal baryon-density...
s-Process Nucleosynthesis in Low-Metallicity Stars (2002)
Iwamoto, Nobuyuki, Kajino, Toshitaka, Mathews, Grant J., Fujimoto, Masayuki Y., Aoki, Wako
We have made a parametric study of s-process nucleosynthesis in the metal poor ([Fe/H]=-2.7) stars LP625-44 and LP706-7. We find that a high neutron exposure and a small overlap factor are necessary...
Rapid rotation of ultra-Li-depleted halo stars and their association with blue stragglers (2002)
Ryan, Sean G., Gregory, Scott G., Kolb, Ulrich, Beers, Timothy C., Kajino, Toshitaka
Observations of eighteen halo main-sequence-turnoff stars, four of which are extremely deficient in Li, show that three of the Li-poor ones have substantial line broadening. We attribute this to...
Neutron Capture Elements in s-Process-Rich, Very Metal-Poor Stars (2001)
Aoki, Wako, Ryan, Sean G., Norris, John E., Beers, Timothy C., Ando, Hiroyasu, Iwamoto, Nobuyuki, ...
We report abundance estimates for neutron-capture elements, including lead (Pb), and nucleosynthesis models for their origin, in two carbon-rich, very metal-poor stars, LP625-44 and LP706-7. These...
Wanajo, Shinya, Kajino, Toshitaka, Mathews, Grant J., Otsuki, Kaori
We present calculations of r-process nucleosynthesis in neutrino-driven winds from the nascent neutron stars of core-collapse supernovae. A full dynamical reaction network for both the alpha-rich...
Abundances and Evolution of Lithium in the Galactic Halo and Disk (2000)
Ryan, Sean G., Kajino, Toshitaka, Beers, Timothy C., Suzuki, Takeru Ken, Romano, Donatella, Matteucci, Francesca, ...
We have measured the Li abundance of 18 stars with -2
Ultra-Lithium-Deficient Halo Stars and Blue Stragglers: A Common Origin? (2000)
Ryan, Sean G., Beers, Timothy C., Kajino, Toshitaka, Rosolankova, Katarina
We present data for four ultra-Li-deficient, warm, halo stars. The Li deficiency of two of these is a new discovery. Three of the four stars have effective temperatures Teff ~ 6300 K, in contrast to...
Impact of Few-Body Reactions on Explosive Nucleosynthesis: The Big-Bang and Supernovae (2000)
Kajino, Toshitaka, Otsuki, Kaori, Wanajo, Shin-ya, Orito, Manabu, Mathews, Grant J.
We study the few body reactions in explosive nucleosynthesis of light-to-heavy mass elements in various astrophysical conditions. In neutrino-driven winds of gravitational core collapse of SNeII,...
Otsuki, Kaori, Tagoshi, Hideyuki, Kajino, Toshitaka, Wanajo, Shin-ya
Neutrino-driven wind from young hot neutron star, which is formed by supernova explosion, is the most promising candidate site for r-process nucleosynthesis. We study general relativistic effects on...
Tokuhisa, Akira, Kajino, Toshitaka
Gamma-ray bursts (GRBs) are presumed to be powered by still unknown central engines for the timescales in the range $1ms \sim$ a few s. We propose that the GRB central engines would be a viable site...
Evolution of Beryllium and Boron in the Inhomogeneous Early Galaxy (1999)
Suzuki, Takeru Ken, Yoshii, Yuzuru, Kajino, Toshitaka
A model of supernova-driven chemical evolution of the Galactic halo, recently proposed by Tsujimoto, Shigeyama, & Yoshii (1999, ApJL, 519, 64), is extended in order to investigate the evolution of...
QCD Phase Transition at high Temperature in Cosmology (1996)
Suganuma, Hideo, Ichie, Hiroko, Monden, Hideko, Sasaki, Shoichi, Orito, Manabu, Yamamoto, Tadahiro, ...
The cosmological QCD phase transition is studied in terms of the color confinement at finite temperature using the dual Higgs theory of QCD. The confinement force is largely reduced at high...