Improved constraints on cosmic birefringence from the WMAP and <i>Planck</i> cosmic microwave background polarization data

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