Cosmic Birefringence from Planck Data Release 4

TL;DR

This paper investigates cosmic birefringence using Planck Data Release 4, finding initial signals that are likely affected by foreground emissions, and emphasizes the need for better foreground modeling before claiming cosmological implications.

Contribution

The study provides a new measurement of cosmic birefringence with Planck data and introduces two methods to model and mitigate foreground effects affecting the polarization signal.

Findings

Measured birefringence angle of 0.30±0.11 degrees.

Foreground polarization significantly influences the birefringence measurement.

Further foreground modeling is necessary for definitive cosmological conclusions.

Abstract

We search for the signature of parity-violating physics in the cosmic microwave background, called cosmic birefringence, using the Planck data release 4. We initially find a birefringence angle of $\beta=0.30\pm0.11$ (68% C.L.) for nearly full-sky data. The values of $\beta$ decrease as we enlarge the Galactic mask, which can be interpreted as the effect of polarized foreground emission. Two independent ways to model this effect are used to mitigate the systematic impact on $\beta$ for different sky fractions. We choose not to assign cosmological significance to the measured value of $\beta$ until we improve our knowledge of the foreground polarization.