New Extraction of the Cosmic Birefringence from the Planck 2018 Polarization Data

We search for evidence of parity-violating physics in the Planck 2018 polarization data and report on a new measurement of the cosmic birefringence angle beta. The previous measurements are limited by the systematic uncertainty in the absolute polarization angles of the Planck detectors. We mitigate this systematic uncertainty completely by simultaneously determining beta and the angle miscalibration using the observed cross-correlation of the E- and B-mode polarization of the cosmic microwave background and the Galactic foreground emission. We show that the systematic errors are effectively mitigated and achieve a factor-of-2 smaller uncertainty than the previous measurement, finding beta = 0.35 +/- 0.14 deg (68% C.L.), which excludes beta = 0 at 99.2% C.L. This corresponds to the statistical significance of 2.4s.