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Register a new userLarge-scale acoustic peak shift in the Planck CMB data
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Cosmic microwave background (CMB) temperature anisotropies encode the history of the universe, which manifest itself in the angular power spectrum. We test the angular power spectra of small patches from the ESA $textit{Planck}$ data. Known variations in the power spectra from small patches reveal informative details such as the gravitational lensing and the Doppler boosting effect. We compute the relative shifts of power spectra via comparing patches selected randomly from the CMB. We visualize the relative shifts on a full-sky HEALPix grid (a feature map) and analyze the statistical properties on the full-sky map. We find the regions contain the Cold Spot and the Draco supervoid have large relative shifts to large scales. We also find a dipole on the generated feature map comparing with simulations. We discuss possible ways to resolve this dipole on the feature map, including foregrounds, solar dipole systematics, and the uncertainty in our method.
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We develop a method to constrain non-isotropic features of Cosmic Microwave Background (CMB) polarization, of a type expected to arise in some models describing quantum gravity effects on light propagation. We describe the expected signatures of this kind of anomalous light propagation on CMB photons, showing that it will produce a non-isotropic birefringence effect, i.e. a rotation of the CMB polarization direction whose observed amount depends in a peculiar way on the observation direction. We also show that the sensitivity levels expected for CMB polarization studies by the emph{Planck} satellite are sufficient for testing these effects if, as assumed in the quantum-gravity literature, their magnitude is set by the minute Planck length.
Measurement of the acoustic peaks of the cosmic microwave background (CMB) temperature anisotropies has been instrumental in deciding the geometry and content of the universe. Acoustic peak positions vary in different parts of the sky due to statistical fluctuation. We present the statistics of the peak positions of small patches from ESA Planck data. We found that the peak positions have significantly high variance compared to the 100 CMB simulations with best-fit LambdaCDM model with lensing and Doppler boosting effects included. Examining individual patches, we found the one containing the mysterious Cold Spot, an area near the Eridanus constellation where the temperature is significantly lower than Gaussian theory predicts, displays large synchronous shift of peak positions towards smaller multipole numbers with significance lower than 1.11x 10^{-4}. The combination of large synchronous shifts in acoustic peaks and lower than usual temperature at the Cold Spot area results in a 4.73-sigma detection (significance p~ 1.11x 10^{-6}) against the LambdaCDM model. And it was already reported in Finelli et al. (2016) that in the WISE-2MASS galaxy catalog at z<0.3 the Cold Spot region is surrounded by surprisingly large underdense regions around 15 degs in radius, which are found to be in the same square patch. Thus we propose there is some extra localized unknown energy to stretch out the space in the transverse direction around the Cold Spot area to simultaneously account for the Cold Spot, excessive shift of the acoustic peaks, and the large underdense regions.
CMB angular spectrum measurements suggest a flat universe. This paper clarifies the relation between geometry and the spherical harmonic index of the first acoustic peak ($ell_{peak}$). Numerical and analytic calculations show that $ell_{peak}$ is approximately a function of $Omega_K/Omega_M$ where $Omega_K$ and $Omega_M$ are the curvature ($Omega_K > 0$ implies an open geometry) and mass density today in units of critical density. Assuming $Omega_K/Omega_M ll 1$, one obtains a simple formula for $ell_{peak}$, the derivation of which gives another perspective on the widely-recognized $Omega_M$-$Omega_Lambda$ degeneracy in flat models. This formula for near-flat cosmogonies together with current angular spectrum data yields familiar parameter constraints.
Weak lensing peak counts are a powerful statistical tool for constraining cosmological parameters. So far, this method has been applied only to surveys with relatively small areas, up to several hundred square degrees. As future surveys will provide weak lensing datasets with size of thousands of square degrees, the demand on the theoretical prediction of the peak statistics will become heightened. In particular, large simulations of increased cosmological volume are required. In this work, we investigate the possibility of using simulations generated with the fast Comoving-Lagrangian acceleration (COLA) method, coupled to the convergence map generator Ufalcon, for predicting the peak counts. We examine the systematics introduced by the COLA method by comparing it with a full TreePM code. We find that for a 2000 deg$^2$ survey, the systematic error is much smaller than the statistical error. This suggests that the COLA method is able to generate promising theoretical predictions for weak lensing peaks. We also examine the constraining power of various configurations of data vectors, exploring the influence of splitting the sample into tomographic bins and combining different smoothing scales. We find the combination of smoothing scales to have the most constraining power, improving the constraints on the $S_8$ amplitude parameter by at least 40% compared to a single smoothing scale, with tomography brining only limited increase in measurement precision.
Several unexpected features have been observed in the microwave sky at large angular scales, both by WMAP an by Planck. Among those features is a lack of both variance and correlation on the largest angular scales, alignment of the lowest multipole moments with one another and with the motion and geometry of the Solar System, a hemispherical power asymmetry or dipolar power modulation, a preference for odd parity modes and an unexpectedly large cold spot in the Southern hemisphere. The individual p-values of the significance of these features are in the per mille to per cent level, when compared to the expectations of the best-fit inflationary $Lambda$CDM model. Some pairs of those features are demonstrably uncorrelated, increasing their combined statistical significance and indicating a significant detection of CMB features at angular scales larger than a few degrees on top of the standard model. Despite numerous detailed investigations, we still lack a clear understanding of these large-scale features, which seem to imply a violation of statistical isotropy and scale invariance of inflationary perturbations. In this contribution we present a critical analysis of our current understanding and discuss several ideas of how to make further progress.
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