126 research outputs found
Geometric Gaussianity and Non-Gaussianity in the Cosmic Microwave Background
In this paper, Gaussianity of eigenmodes and non-Gaussianity in the Cosmic
Microwave Background (CMB) temperature fluctuations in two smallest compact
hyperbolic (CH) models are investigated. First, it is numerically found that
the expansion coefficients of low-lying eigenmodes on the two CH manifolds
behave as if they are Gaussian random numbers at almost all the places. Next,
non-Gaussianity of the temperature fluctuations in the (l,m) space in these
models is studied. Assuming that the initial fluctuations are Gaussian, the
real expansion coefficients b_{l m} of the temperature fluctuations in the sky
are found to be distinctively non-Gaussian. In particular, the cosmic variances
are found to be much larger than that for Gaussian models. On the other hand,
the anisotropic structure is vastly erased if one averages the fluctuations at
a number of different observing points because of the Gaussian
pseudo-randomness of the eigenmodes. Thus the dominant contribution to the
two-point correlation functions comes from the isotropic terms described by the
angular power spectra C_l. Finally, topological quantities: the total length
and the genus of isotemperature contours are investigated. The variances of
total length and genus at high and low threshold levels are found to be
considerably larger than that of Gaussian models while the means almost agree
with them.Comment: 22 pages, 18 figures (eps files). Typos correcte
Probing the Origin of the Large-angle CMB Anomalies
It has been argued that the large-angle cosmic microwave background
anisotropy has anomalies at 3-sigma level. We review various proposed ideas to
explain the origin of the anomalies and discuss how we can constrain the
proposed models using future observational data.Comment: 5 page
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
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