The axis of evil - a polarization perspective

TL;DR

This study investigates the alignment of the axis of evil in CMB temperature and polarization data, finding partial alignment and assessing the likelihood of chance occurrence, with implications for understanding cosmic anisotropies.

Contribution

It introduces an analysis of uncorrelated polarization data to test the cosmological origin of the axis of evil, providing new insights into its alignment and statistical significance.

Findings

Quadrupole axis of uncorrelated polarization roughly aligns with the axis of evil.

Octopole axis does not show significant alignment.

Chance probability of observed alignment is about 50% in an isotropic universe.

Abstract

We search for an unusual alignment of the preferred axes of the quadrupole and octopole, the so-called axis of evil, in the CMB temperature and polarization data from WMAP. We use the part of the polarization map which is uncorrelated with the temperature map as a statistically independent probe of the axis of evil, which helps to assess whether the latter has a cosmological origin or if is a mere chance fluctuation in the temperature. Note, though, that for certain models creating a preferred axis in the temperature map, we would not expect to see the axis in the uncorrelated polarization map. We find that the axis of the quadrupole of the uncorrelated polarization map roughly aligns with the axis of evil within our measurement precision, whereas the axis of the octopole does not. However, with our measurement uncertainty, the probability of such a scenario to happen by chance in an isotropic universe is of the order of 50 per cent. We also find that the so-called cold spot present in the CMB temperature map is even colder in the part of the temperature map which is uncorrelated with the polarization, although there is still a large uncertainty in the latter. Therefore, our analysis of the axis of evil and a future analysis of the cold spot in the uncorrelated temperature data will strongly benefit from the polarization data expected from the Planck satellite.