The T-E correlation coefficient of Planck legacy data

TL;DR

This paper introduces a new observable, the T-E correlation coefficient, which is robust against instrumental systematics and used to analyze Planck CMB data for deviations from the standard cosmological model.

Contribution

The paper defines and studies the properties of the T-E correlation coefficient, demonstrating its insensitivity to certain systematics and applying it to Planck data analysis.

Findings

The T-E correlation coefficient is unaffected by calibration and beam errors.

Planck data's T-E correlation aligns with the ΛCDM model.

The observable's statistical properties are derived and validated.

Abstract

Testing deviations from the $\Lambda$CDM model using the Cosmic Microwave Background (CMB) power spectra requires a pristine understanding of instrumental systematics. In this work we discuss the properties of a new observable ${\cal R}^{TE}_{\ell}$, the correlation coefficient of temperature and E modes. We find that this observable is mostly unaffected by systematics introducing multiplicative biases such as errors in calibration, polarisation efficiency, beam and transfer function measurements. We discuss the dependency of this observable on the cosmological model and derive its statistical properties. We then compute the T-E correlation coefficients of Planck legacy data and compare them with expectations from the Planck best-fit $\Lambda$CDM and foreground model.