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Extended Slow-Roll Conditions and Primordial Fluctuations: Multiple Scalar Fields and Generalized Gravity
Takeshi Chiba, Masahide Yamaguchi
As an extension of our previous study, we derive slow-roll conditions for multiple scalar fields which are non-minimally coupled with gravity and for generalized gravity theories o…
Extended Slow-Roll Conditions and Rapid-Roll Conditions
Takeshi Chiba, Masahide Yamaguchi
We derive slow-roll conditions for a scalar field which is non-minimally coupled with gravity in a consistent manner and express spectral indices of scalar/tensor perturbations in…
Precision calculations of the gravitational wave background spectrum from inflation
Sachiko Kuroyanagi, Takeshi Chiba, Naoshi Sugiyama
The spectrum of the gravitational wave background originating from quantum fluctuations during inflation is calculated numerically for various inflation models over a wide range of…
A Null Test of the Cosmological Constant
Takeshi Chiba, Takashi Nakamura
We provide a consistency relation between cosmological observables in general relativity with the cosmological constant. Breaking of this relation at any redshift would imply the b…
A Consistency Relation in Cosmology
Takeshi Chiba, Ryuichi Takahashi
We provide a consistency relation between cosmological observables in general relativity without relying on the equation of state of dark energy. The consistency relation should be…
Weak Lensing of Galaxy Clusters in MOND
Ryuichi Takahashi, Takeshi Chiba
We study weak gravitational lensing of galaxy clusters in terms of the MOND (MOdified Newtonian Dynamics) theory. We calculate shears and convergences of background galaxies for th…
Solar System constraints to general f(R) gravity
Takeshi Chiba, Tristan L. Smith, Adrienne L. Erickcek
It has been proposed that cosmic acceleration or inflation can be driven by replacing the Einstein-Hilbert action of general relativity with a function f(R) of the Ricci scalar R.…
w and w' of Scalar Field Models of Dark Energy
Takeshi Chiba
Important observables to reveal the nature of dark energy are the equation of state and its time derivative in units of the Hubble time . Recently, it is shown that the sim…
Classifying the Future of Universes with Dark Energy
Takeshi Chiba, Ryuichi Takahashi, Naoshi Sugiyama
We classify the future of the universe for general cosmological models including matter and dark energy. If the equation of state of dark energy is less then -1, the age of the uni…
Does Positronium Form in the Universe ?
Takeshi Chiba, Naoshi Sugiyama
Positronium (the bound state of electron and positron) has been thought to be formed after proton decay (yr) through collisional recombination and then decays by pair ann…
WMAP constraints on scalar-tensor cosmology and the variation of the gravitational constant
Ryo Nagata, Takeshi Chiba, Naoshi Sugiyama
We present observational constraints on a scalar-tensor gravity theory by test for CMB anisotropy spectrum. We compare the WMAP temperature power spectrum with the harmonic a…
1/R gravity and Scalar-Tensor Gravity
Takeshi Chiba
We point out that extended gravity theories, the Lagrangian of which is an arbitrary function of scalar curvature , are equivalent to a class of the scalar tensor theories of gr…
Supernova Cosmology and the Fine Structure Constant
Takeshi Chiba, Kazunori Kohri
We study the dependence of the peak luminosity of Type Ia supernovae on the fine structure constant . We find that decreasing (increasing) enhances (reduces) the luminosity.…
Observational Consequences of Evolution of Primordial Fluctuations in Scalar-Tensor Cosmology
Ryo Nagata, Takeshi Chiba, Naoshi Sugiyama
Evolution of primordial fluctuations in a Brans-Dicke type scalar-tensor gravity theory is comprehensively investigated. The harmonic attractor model, in which the scalar field has…
Tracking K-essence
Takeshi Chiba
We derive a condition for converging a common evolutionary track for k-essence (a scalar field dark energy with non-canonical kinetic terms). For the Lagrangian density V(phi)W(X)…
Extended Quintessence and its Late-time Domination
Takeshi Chiba
Various astronomical observations point towards the evidence for dark energy. One of the most mysterious problem is the coincidence problem: why dark energy becomes dominant only r…
Lens Model Degeneracy and Cosmological Tests by Strong Gravitational Lensing
Takeshi Chiba, Ryuichi Takahashi
We estimate the sensitivity of lensing observables to the parameters in the lens model (isothermal sphere/Navarro-Frenk-White profile) parameters and to cosmological parameters. We…
Gravitational Lens Statistics and The Density Profile of Dark Halos
Ryuichi Takahashi, Takeshi Chiba
We investigate the influence of the inner profile of lens objects on gravitational lens statistics taking into account of the effect of magnification bias and both the evolution an…
Determining the Equation of State of the Expanding Universe Using a New Independent Variable
Takashi Nakamura, Takeshi Chiba
To determine the equation of state of the universe, we propose to use a new independent variable , where and are the present Hubble pa…
Kinetically Driven Quintessence
Takeshi Chiba, Takahiro Okabe, Masahide Yamaguchi
Recently, a novel class of models for inflation has been found in which the inflationary dynamics is driven solely by (non-canonical) kinetic terms rather than by potential terms.…
Determining the Equation of State of the Expanding Universe: Inverse Problem in Cosmology
Takashi Nakamura, Takeshi Chiba
Even if the luminosity distance as a function of redshift is obtained accurately using, for example, Type Ia supernovae, the equation of state of the Universe cannot be determined…
The Luminosity Distance, the Equation of State, and the Geometry of the Universe
Takeshi Chiba, Takashi Nakamura
The second derivative of the luminosity distance with respect to the redshift is written in terms of the deceleration parameter . We point out that the third derivative contai…
Black Hole Binary Formation in the Expanding Universe --- Three Body Problem Approximation ---
Kunihito Ioka, Takeshi Chiba, Takahiro Tanaka +1
We study black hole MACHO binary formation through three-body interactions in the early universe at s. The probability distribution functions of the eccentricity and…
Observational tests of x-matter models
Takeshi Chiba, Naoshi Sugiyama, Takashi Nakamura
We study gravitational lensing statistics, matter power spectra and the angular power spectra of the cosmic microwave background (CMB) radiation in x-matter models. We adopt an equ…