Polarisation as a tracer of CMB anomalies: Planck results and future forecasts

TL;DR

This paper introduces a new estimator combining temperature and polarisation data to analyze CMB anomalies, showing polarisation's potential to enhance anomaly detection in future measurements like LiteBIRD.

Contribution

A novel one-dimensional estimator that jointly uses TT, TE, and EE spectra to assess CMB anomalies, incorporating polarisation data into the analysis.

Findings

Planck polarisation data slightly increases anomaly significance.

Future missions could significantly boost polarisation's role in anomaly detection.

Polarisation may be crucial for understanding large-scale CMB features.

Abstract

The lack of power anomaly is an intriguing feature at the largest angular scales of the CMB anisotropy temperature pattern, whose statistical significance is not strong enough to claim any new physics beyond the standard cosmological model. We revisit the former statement by also considering polarisation data. We propose a new one-dimensional estimator which takes jointly into account the information contained in the TT, TE and EE CMB spectra. By employing this estimator on Planck 2015 low-$\ell$ data, we find that a random $\Lambda$CDM realisation is statistically accepted at the level of $3.68 \%$. Even though Planck polarisation contributes a mere $4 \%$ to the total information budget, its use pushes the lower-tail-probability down from the $7.22 \%$ obtained with only temperature data. Forecasts of future CMB polarised measurements, as e.g. the LiteBIRD satellite, can increase the polarisation contribution up to $6$ times with respect to Planck at low-$\ell$. We argue that the large-scale E-mode polarisation may play an important role in analysing CMB temperature anomalies with future mission.