550 research outputs found
Third-Order Density Perturbation and One-Loop Power Spectrum in Dark-Energy-Dominated Universe
We investigate the third-order density perturbation and the one-loop
correction to the linear power spectrum in the dark-energy cosmological model.
Our main interest is to understand the dark-energy effect on baryon acoustic
oscillations in a quasi-nonlinear regime (/Mpc). Analytical
solutions and simple fitting formulae are presented for the dark-energy model
with the general time-varying equation of state . It turns out that the
power spectrum coincides with the approximate result based on the EdS (Einstein
de-Sitter) model within 1% for Mpc at in the WMAP (Wilkinson
Microwave Anisotropy Probe) 5yr best-fitting cosmological model, which suggests
that the cosmological dependence is very small.Comment: 11 pages, Prog. Ther. Phys. in press, minor changes, references adde
Weak Lensing by Intergalactic Mini-Structures in Quadruple Lens Systems: Simulation and Detection
We investigate the weak lensing effects of line-of-sight structures on
quadruple images in quasar-galaxy strong lens systems based on N-body and
ray-tracing simulations that can resolve halos with a mass of 10^5 solar mass.
The intervening halos and voids disturb the magnification ratios of lensed
images as well as their relative positions due to lensing. The magnification
ratios typically change by O(10%) when the shifts of relative angular positions
of lensed images are constrained to <0.004 arcsec. The constrained amplitudes
of projected density perturbations due to line-of-sight structures are O(10^8)
solar mass per arcsec^2. These results are consistent with our new analytical
estimate based on the two-point correlation of density fluctuations. The
observed mid-infrared (MIR) flux ratios for 6 quasar-galaxy lens systems with
quadruple images agree well with the numerically estimated values without
taking into account of subhalos residing in the lensing galaxies. We find that
the constrained mean amplitudes of projected density perturbations in the
line-of-sight are negative, which suggests that the fluxes of lensed images are
perturbed mainly by minivoids and minihalos in underdense regions. We derive a
new fitting formula for estimating the probability distribution function of
magnification perturbation. We also find that the mean amplitude of
magnification perturbation roughly equals the standard deviation regardless of
the model parameters.Comment: 22 pages, 15 figures, accepted for publication in MNRA
Constraints on small-scale cosmological fluctuations from SNe lensing dispersion
We provide predictions on small-scale cosmological density power spectrum
from supernova lensing dispersion. Parameterizing the primordial power spectrum
with running and running of running of the spectral index, we
exclude large positive and parameters which induce too large
lensing dispersions over current observational upper bound. We ran cosmological
N-body simulations of collisionless dark matter particles to investigate
non-linear evolution of the primordial power spectrum with positive running
parameters. The initial small-scale enhancement of the power spectrum is
largely erased when entering into the non-linear regime. For example, even if
the linear power spectrum at is enhanced by orders
of magnitude, the enhancement much decreases to a factor of at late time
(). Therefore, the lensing dispersion induced by the dark matter
fluctuations weakly constrains the running parameters. When including
baryon-cooling effects (which strongly enhance the small-scale clustering), the
constraint is comparable or tighter than the PLANCK constraint, depending on
the UV cut-off. Further investigations of the non-linear matter spectrum with
baryonic processes is needed to reach a firm constraint.Comment: 11 pages, 9 figures. Submitted to MNRA
Amplitude and Phase Fluctuations for Gravitational Waves Propagating through Inhomogeneous Mass Distribution in the Universe
When a gravitational wave (GW) from a distant source propagates through the
universe, its amplitude and phase change due to gravitational lensing by the
inhomogeneous mass distribution. We derive the amplitude and phase
fluctuations, and calculate these variances in the limit of a weak
gravitational field of density perturbation. If the scale of the perturbation
is smaller than the Fresnel scale ( is the
GW frequency), the GW is not magnified due to the diffraction effect. The rms
amplitude fluctuation is for Hz, but it is reduced less
than 5% for a very low frequency of Hz. The rms phase
fluctuation in the chirp signal is radian at LISA frequency band
( Hz). Measurements of these fluctuations will provide
information about the matter power spectrum on the Fresnel scale pc.Comment: 6 pages, 6 figures, refferences added, accepted for publication in
Ap
Determination of the equation of the state of the Universe using ~ 0.1 Hz Gravitational Wave Detectors
We show that ten(one) years operation of the ultimate DECIGO (DECihertz
Interferometer Gravitational wave Observatory) can determine the cosmic
equation of the state with such accuracy that 0.06%(3%), 0.08%(4%) and
0.06%(3%) for , and , respectively. In more realistic
case of practical DECIGO or BBO (Big Bang Observer), will be determined
within by ten years observation assuming the flat universe model.
Hence, the DECIGO or BBO will give an independent determination of the cosmic
equation of the state.Comment: 9 pages, 6 figures; accepted for publication in Prog. Theor. Phy
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