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

Measuring Line-of-sight Distances to Haloes with Astrometric Lensing B-mode

Relative astrometric shifts between multiply lensed images provide a valuable tool to investigate haloes in the intergalactic space. In strong lens systems in which a single lens plays the primary role in producing multiple images, the gravitational force exerted by line-of-sight (LOS) haloes can slightly change the relative positions of multiply lensed images produced by the dominant lens. In such cases, a LOS halo positioned sufficiently far from the dominant lens along the LOS can create a pattern in the reduced deflection angle that corresponds to the B-mode (magnetic or divergence-free mode). By measuring both the B-mode and E-mode (electric or rotation-free mode), we can determine the LOS distance ratios, as well as the 'bare' convergence and shear perturbations in the absence of the dominant lens. However, scale variations in the distance ratio lead to mass-sheet transformations in the background lens plane, introducing some uncertainty in the distance ratio estimation. This uncertainty can be significantly reduced by measuring the time delays between the lensed images. Additionally, if we obtain the redshift values of both the dominant and perturbing haloes, along with the time delays between the multiply lensed images that are affected by the haloes, the B-mode can break the degeneracy related to mass-sheet transformations in both the foreground and background lens planes. Therefore, measuring the astrometric lensing B-mode has the potential to substantially decrease the uncertainty in determining the Hubble constant.Comment: 15 pages, 16 figure

Weak Lensing by Minifilament or Minivoid as the Origin of Flux-ratio Anomalies in Lensed Quasar MG0414+0534

We explore the weak lensing effects by ministructures in the line-of-sight in a quadruply lensed quasar MG0414+0534 that shows an anomaly in the flux-ratios. We find that the observed flux-ratio anomaly can be explained by a presence of either a minifilament or a minivoid in the line-of-sight with a surface mass density of the order of 10^(8-9) h^(-1) solar mass /arcsec^2 without taking into account any subhalos in the lensing galaxy. The astrometric perturbation by a possible minifilament/minivoid is <~ 0.001 arcsec and the amplitudes of convergence perturbations due to these perturbers are ~ 0.004-0.008 at the place of an image that shows anomaly. In order to discriminate models with the line-of-sight ministructures from those with a subhalo(s) in the lensing galaxy, we need to precisely measure the projected convergence and shear around the lensing galaxy. The differential magnification effect could break the model degeneracy if the source size is > ~100 pc. Observation at the submillimeter band using interferometers will enable us to determine the origin of anomalies in the flux ratios.Comment: 9 pages, 7 figures, version accepted for publication in MNRA