Improved Constraints on Cosmic Birefringence from the WMAP and Planck Cosmic Microwave Background Polarization Data

Abstract

The observed pattern of linear polarization of the cosmic microwave background (CMB) photons is a sensitive probe of physics violating parity symmetry under inversion of spatial coordinates. A new parity-violating interaction might have rotated the plane of linear polarization by an angle $β$ as the CMB photons have been traveling for more than 13 billion years. This effect is known as "cosmic birefringence." In this paper, we present new measurements of cosmic birefringence from a joint analysis of polarization data from two space missions, Planck and WMAP. This dataset covers a wide range of frequencies from 23 to 353 GHz. We measure $β= 0.342^{\circ\,+0.094^\circ}_{\phantom{\circ\,}-0.091^\circ}$ (68% C.L.) for nearly full-sky data, which excludes $β=0$ at 99.987% C.L. This corresponds to the statistical significance of $3.6σ$. There is no evidence for frequency dependence of $β$. We find a similar result, albeit with a larger uncertainty, when removing the Galactic plane from the analysis.