Cosmic Birefringence from the Planck Data Release 4

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 degrees +/- 0.11 degrees (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.

Automated summary

In this study, we search for parity-violating physics in the cosmic microwave background using Planck data. We find a possible cosmic birefringence effect, but further research is needed to understand its cosmological significance.