Rapid Merger of Binary Primordial Black Holes (2009)
Hayasaki, Kimitake, Takahashi, Keitaro, Sendouda, Yuuiti, Nagataki, Shigehiro
We propose a new scenario for the evolution of a binary of primordial black holes (PBHs). We consider the dynamical friction by ambient dark matter and gravitational interaction between a binary and...
Ando, Masaki, Kawamura, Seiji, Sato, Shuichi, Nakamura, Takashi, Tsubono, Kimio, Araya, Akito, ...
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...
Aoi, Junichi, Murase, Kohta, Takahashi, Keitaro, Ioka, Kunihito, Nagataki, Shigehiro
We revisit the high-energy spectral cutoff originating from the electron-positron pair creation in the prompt phase of gamma-ray bursts (GRBs) with numerical and analytical calculations. We show that...
Possible Effects of Pair Echoes on Gamma-Ray Burst Afterglow Emission (2008)
Murase, Kohta, Zhang, Bing, Takahashi, Keitaro, Nagataki, Shigehiro
High-energy emission from gamma-ray bursts (GRBs) is widely expected but had been sparsely observed until recently when the Fermi satellite was launched. If >TeV gamma rays are produced in GRBs and...
Takahashi, Keitaro, Naruko, Atsushi, Sendouda, Yuuiti, Yamauchi, Daisuke, Yoo, Chul-Moon, Sasaki, Misao
We compute analytically the small-scale temperature fluctuations of cosmic microwave background from cosmic (super-)strings and study the dependence on the string intercommuting probability $P$. We...
Tsutsui, Ryo, Nakamura, Takashi, Yonetoku, Daisuke, Murakami, Toshio, Kodama, Yoshiki, Takahashi, Keitaro
We consider two empirical relations using data only from the prompt emission of Gamma-Ray Bursts (GRBs), peak energy ($E_p$) - peak luminosity ($L_p$) relation (so called Yonetoku relation) and...
Ando, Masaki, Kawamura, Seiji, Nakamura, Takashi, Tsubono, Kimio, Tanaka, Takahiro, Funaki, Ikkoh, ...
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...
The Japanese space gravitational wave antenna; DECIGO (2008)
Kawamura, Seiji, Ando, Masaki, Nakamura, Takashi, Tsubono, Kimio, Tanaka, Takahiro, Funaki, Ikkoh, ...
DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) is the future Japanese space gravitational wave antenna. DECIGO is expected to open a new window of observation for gravitational...
Constraints on $w_0$ and $w_a$ of Dark Energy from High Redshift Gamma Ray Bursts (2008)
Tsutsui, Ryo, Nakamura, Takashi, Yonetoku, Daisuke, Murakami, Toshio, Tanabe, Sachiko, Kodama, Yoshiki, ...
We extend the Hubble diagram up to $z = 5.6$ using 63 gamma-ray bursts (GRBs) via peak energy-peak luminosity relation (so called Yonetoku relation), and obtain constraints on cosmological parameters...
Detectability of Pair Echos from Gamma-Ray Bursts and Intergalactic Magnetic Fields (2008)
Takahashi, Keitaro, Murase, Kohta, Ichiki, Kiyotomo, Inoue, Susumu, Nagataki, Shigehiro
High-energy emission from gamma-ray bursts (GRBs) can give rise to pair echos, i.e. delayed inverse Compton emission from secondary $e^{\pm}$ pairs produced in $\gamma-\gamma$ interactions with...
Murase, Kohta, Takahashi, Keitaro, Inoue, Susumu, Ichiki, Kiyomoto, Nagataki, Shigehiro
More than a dozen blazars are known to be emitters of multi-TeV gamma rays, often with strong and rapid flaring activity. By interacting with photons of the cosmic microwave and infrared backgrounds,...
Electromagnetic properties of the early universe (2008)
Takahashi, Keitaro, Ichiki, Kiyotomo, Sugiyama, Naoshi
Detailed physical processes of magnetic field generation from density fluctuations in the prerecombination era are studied. Solving Maxwell equations and the generalized Ohm's law, the evolutions of...
Behavior of magnetic fields around the cosmic recombination (2008)
Several mechanisms have been proposed to generate primordial magnetic fields and it is often assumed that magnetic fields are not affected by a sharp drop in ionization rate due to the cosmic...
Ichiki, Kiyotomo, Inoue, Susumu, Takahashi, Keitaro
We investigate the delayed, secondary GeV-TeV emission of gamma-ray bursts and its potential to probe the nature of intergalactic magnetic fields. Geometrical effects are properly taken into account...
Electromagnetic Properties of the Early Universe (2007)
Takahashi, Keitaro, Ichiki, Kiyotomo, Sugiyama, Naoshi
Detailed physical processes of magnetic field generation from density fluctuations in the pre-recombination era are studied. Solving Maxwell equations and the generalized Ohm's law, the evolutions of...
Gravitational Wave Spectrum Induced by Primordial Scalar Perturbations (2007)
Baumann, Daniel, Ichiki, Kiyotomo, Steinhardt, Paul J., Takahashi, Keitaro
We derive the complete spectrum of gravitational waves induced by primordial scalar perturbations ranging over all observable wavelengths. This scalar-induced contribution can be computed directly...
Cosmological magnetic fields from nonlinear effects (2007)
Kobayashi, Tsutomu, Maartens, Roy, Shiromizu, Tetsuya, Takahashi, Keitaro
In the standard cosmological model, magnetic fields and vorticity are generated during the radiation era via second-order density perturbations. In order to clarify the complicated physics of this...
Magnetic Field Spectrum at Cosmological Recombination (2007)
Ichiki, Kiyotomo, Takahashi, Keitaro, Sugiyama, Naoshi, Hanayama, Hidekazu, Ohno, Hiroshi
A generation of magnetic fields from cosmological density perturbations is investigated. In the primordial plasma before cosmological recombination, all of the materials except dark matter in the...
Gravitational lensing effects on the gamma-ray burst Hubble diagram (2006)
Oguri, Masamune, Takahashi, Keitaro
Gamma-Ray Bursts (GRBs) offer a potential way to extend the Hubble diagram to very high redshifts and to constrain the nature of dark energy in a way complementary to distant type Ia supernovae....
Cosmological Magnetic Field: a fossil of density perturbations in the early universe (2006)
Ichiki, Kiyotomo, Takahashi, Keitaro, Ohno, Hiroshi, Hanayama, Hidekazu, Sugiyama, Naoshi
The origin of the substantial magnetic fields that are found in galaxies and on even larger scales, such as in clusters of galaxies, is yet unclear. If the second-order couplings between photons and...
Generation of magnetic field from cosmological perturbations (2006)
Takahashi, Keitaro, Ichiki, Kiyotomo, Ohno, Hiroshi, Hanayama, Hidekazu, Sugiyama, Naoshi
We discuss generation of magnetic field from cosmological perturbations. We consider the evolution of three component plasma (electron, proton and photon) evaluating the collision term between...
Biermann Mechanism in Primordial Supernova Remnant and Seed Fields (2005)
Hanayama, Hidekazu, Takahashi, Keitaro, Kotake, Kei, Oguri, Masamune, Ichiki, Kiyotomo, Ohno, Hiroshi
We have studied the generation of magnetic fields by the Biermann mechanism in the pair-instability supernovae explosions of the first stars. The Biermann mechanism produces magnetic fields in the...
Explosion Mechanism, Neutrino Burst, and Gravitational Wave in Core-Collapse Supernovae (2005)
Kotake, Kei, Sato, Katsuhiko, Takahashi, Keitaro
Core-collapse supernovae are among the most energetic explosions in the universe marking the catastrophic end of massive stars. In spite of rigorous studies for several decades, we still don't...
Characterizing a cosmic string with the statistics of string lensing (2005)
Oguri, Masamune, Takahashi, Keitaro
The deep imaging of the field of an observed lensing event by a cosmic string reveals many additional lensing events. We study the statistics of such string lensing. We derive explicit expressions...
Gravity is controlled by cosmological constant (2005)
Iwashita, Yukinori, Shiromizu, Tetsuya, Takahashi, Keitaro, Fujii, Shunsuke
We discuss a Randall-Sundrum-type two D-braneworld model in which D-branes possess different values of the tensions from those of the charges, and derive an effective gravitational equation on the...
Magnetic field generation from cosmological perturbations (2005)
Takahashi, Keitaro, Ichiki, Kiyotomo, Ohno, Hiroshi, Hanayama, Hidekazu
In this letter, we discuss generation of magnetic field from cosmological perturbations. We consider the evolution of three component plasma (electron, proton and photon) evaluating the collision...
Biermann Mechanism in Primordial Supernova Remnant and Seed Magnetic Fields (2005)
Hanayama, Hidekazu, Takahashi, Keitaro, Kotake, Kei, Oguri, Masamune, Ichiki, Kiyotomo, Ohno, Hiroshi
We study generation of magnetic fields by the Biermann mechanism in the pair-instability supernovae explosions of first stars. The Biermann mechanism produces magnetic fields in the shocked region...
An Analytic Model of Superclusters (2004)
Oguri, Masamune, Takahashi, Keitaro, Ichiki, Kiyotomo, Ohno, Hiroshi
We construct an analytic model for the mass distributions of superclusters and clusters in each supercluster. Our model is a modification of the Press-Schechter theory, and defines superclusters as...
Asymmetric D-braneworld (2004)
Takahashi, Keitaro, Shiromizu, Tetsuya
In recent papers on Randall-Sundrum D-braneworld model with Z_2 symmetry, it was shown that the effective gravity does not work as usual, that is, the gravity does not couple to the gauge field...
Gravity in Randall-Sundrum two D-brane model (2004)
Shiromizu, Tetsuya, Takahashi, Keitaro, Himemoto, Yoshiaki, Yamamoto, Shuto
We analyse Randall-Sundrum two D-brane model by linear perturbation and then consider the linearised gravity on the D-brane. The qualitative contribution from the Kaluza-Klein modes of gauge fields...
Randall-Sundrum two D-brane model (2004)
Shiromizu, Tetsuya, Himemoto, Yoshiaki, Takahashi, Keitaro
In Randall-Sundrum two D-brane system we derive the gravitational theory on the branes. It is turned out from the consistency that one D-brane has the negative tension brane under Randall-Sundrum...
Acoustic causality in relativistic shells (2004)
Kinoshita, Shunichiro, Sendouda, Yuuiti, Takahashi, Keitaro
The motion of sound waves propagating in the perfect fluid with inhomogeneous background flow is effectively described as a massless scalar field on a curved space-time. This effective geometry is...
WMAP Constraints on Decaying Cold Dark Matter (2004)
Ichiki, Kiyotomo, Oguri, Masamune, Takahashi, Keitaro
We re-formulate cosmological perturbations in the decaying cold dark matter model, and calculate cosmological microwave background (CMB) anisotropies. By comparing our theoretical predictions with...
Sunyaev-Zel'dovich power spectrum with decaying cold dark matter (2003)
Takahashi, Keitaro, Oguri, Masamune, Ichiki, Kiyotomo
Recent studies of structures of galaxies and clusters imply that dark matter might be unstable and decay with lifetime $\Gamma^{-1}$ about the age of universe. We study the effects of the decay of...
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...
D-braneworld cosmology II: Higher order corrections (2003)
Uesugi, Tomoko, Shiromizu, Tetsuya, Torii, Takashi, Takahashi, Keitaro
We investigate braneworld cosmology based on the D-brane initiated in our previous paper. The brane is described by a Born-Infeld action and the gauge field is contained. The higher order corrections...
Exactly solvable model for cosmological perturbations in dilatonic brane worlds (2003)
Koyama, Kazuya, Takahashi, Keitaro
We construct a model where cosmological perturbations are analytically solved based on dilatonic brane worlds. A bulk scalar field has an exponential potential in the bulk and an exponential coupling...
Supernova Neutrinos, Neutrino Oscillations, and the Mass of the Progenitor Star (2003)
Takahashi, Keitaro, Sato, Katsuhiko, Burrows, Adam, Thompson, Todd A.
We investigate the initial progenitor mass dependence of the early-phase neutrino signal from supernovae taking neutrino oscillations into account. The early-phase analysis has advantages in that it...
Decaying Cold Dark Matter and the Evolution of the Cluster Abundance (2003)
Oguri, Masamune, Takahashi, Keitaro, Ohno, Hiroshi, Kotake, Kei
The cluster abundance and its redshift evolution are known to be a powerful tool to constrain the amplitude of mass fluctuations \sigma_8 and the mass density parameter \Omega_m0. We study the impact...
Primordial fluctuations in bulk inflaton model (2003)
Koyama, Kazuya, Takahashi, Keitaro
An inflationary brane model driven by a bulk inflaton with exponential potential is proposed. We find a family of exact solutions that describe power-law inflation on the brane. These solutions...
Effective theory for close limit of two branes (2002)
Shiromizu, Tetsuya, Koyama, Kazuya, Takahashi, Keitaro
We discuss the effective theory for the close limit of two branes in a covariant way. To do so we solve the five dimensional Einstein equation along the direction of the extra dimension. Using the...
Takahashi, Saori, Ogasawara, Hironobu, Takahashi, Keitaro, Hori, Kazuyukd, Saito, Kyuichi, Mori, Katsumi
Renin binding protein (RnBP), a cellular renin inhibitor, has been identified as the enzyme AT-acetyl-D-glucosamine (GlcNAc) 2-epimerase. Our recent studies demonstrated that rat GlcNAc 2-epimerase...
Nagataki, Shigehiro, Takahashi, Keitaro
We estimate the fluxes of very high energy (VHE) gamma-rays and neutrinos from the Galactic Center which are by-products of the hadronic interactions between primary protons which are accelerated up...
Takahashi, Saori, Hori, Kazuyuki, Takahashi, Keitaro, Ogasawara, Hironobu, Tomatsu, Makoto, Saito, Kyuichi
Renin-binding protein (RnBP) is an endogenous renin inhibitor originally isolated from porcine kidney as a complex of renin, so-called high molecular weight (HMW) renin. Our recent studies...
Takahashi, Saori, Takahashi, Keitaro, Kaneko, Takahiro, Ogasawara, Hironobu, Shindo, Sho, Saito, Kyuichi, ...
Renin-binding protein (RnBP) is an endogenous renin inhibitor originally isolated from porcine kidney. It was recently identified as the enzyme N-acetyl-D-glucosamine (GlcNAc) 2-epimerase [Takahashi,...
Takahashi, Saori, Takahashi, Keitaro, Raneko, Takahiro, Ogasawara, Hironobu, Shindo, Sho, Saito, Kyuichi, ...
Renin binding protein (RnBP) is a proteinous renin inhibitor firstly isolated from porcine kidney. Recently, the protein was identified as the enzyme, N-acetyl-D-glucosamine (GlcNAc) 2-epimerase. The...
Human Renin-Binding Protein Is the Enzyme N-Acetyl-D-Glucosamine 2-Epimerase (1999)
Takahashi, Saori, Takahashi, Keitaro, Kaneko, Takahiro, Ogasawara, Hironobu, Shindo, Sho, Kobayashi, Mikihiko
The existence of human renin-binding protein (RnBP) in the kidney has been shown by the isolation and characterization of a complex of porcine renin-human RnBP [S. Takahashi et al. (1985) J. Biochem....