Probing the statistical isotropy of the universe with Planck data of the cosmic microwave background

Abstract

We study the angular distribution of temperature fluctuations in the cosmic microwave background (CMB) to probe the statistical isotropy of the universe by using precise full-sky CMB data with a model-independent approach. We investigated the temperature-temperature angular correlations in the four Planck foreground-cleaned CMB maps that were released recently. We performed a directional analysis on the CMB sphere to search directions in which the temperature-temperature angular correlations are extreme. Our analyses confirm a preferred axis in the CMB sphere, pointing in the direction $(l,b) circ circ )$, at the $98<!PCT!> -99<!PCT!>$ confidence level. In this direction, the CMB angular correlations exceed the antipodal direction most strongly. This preferred direction is unexpected in the Lambda CDM cosmological model and represents a significant deviation from results obtained by applying the same procedure to simulated statistically isotropic CMB maps. This result confirms the north-south asymmetry in the most recent Planck data. This phenomenon is one of the previously reported CMB anomalies. We performed a robust detection of the north-south asymmetry in the temperature-temperature angular correlations, with a slightly different statistical significance, in the four Planck foreground-cleaned CMB maps. Moreover, we performed consistency tests by adding foreground and noise, both Planck data products, to the CMB map we studied, and we also investigated and discarded possible bias in our method. After these detailed analyses, we conclude that the north-south asymmetry phenomenon is present with a high statistical significance in the Planck CMB maps we studied. This result confirms previous reports in the literature in the past 20 years.

Bulk Flow Motion Detection in the Local Universe with Pantheon+ Type Ia Supernovae

“…Our analyses differ from other studies in various aspects. First, our methodology follows previous studies looking for preferred directions on the sky using several cosmic tracers (Bernui et al 2008;Marques et al 2018;Kester et al 2023); second, to avoid systematics from different observables, we use only SNe Ia data from Pantheon+; this choice is a challenge due to the possibility of having few SNe in some directions of the sky; third, we measure H 0 and its uncertainty in a set of N directions, which covers the celestial sphere, performing a best-fit procedure using the Pantheon+ catalog and its covariance matrix, without cosmological model assumptions; fourth, we perform consistency and robustness tests to support our analyses and results.…”