Constraints on cosmological birefringence from Planck and Bicep2/Keck data

Abstract

The polarization of cosmic microwave background (CMB) can be used to constrain cosmological birefringence, the rotation of the linear polarization of CMB photons potentially induced by parity violating physics beyond the standard model. This effect produces non-null CMB cross correlations between temperature and B mode-polarization, and between E- and B-mode polarization. Both cross-correlations are otherwise null in the standard cosmological model. We use the recently released 2015 Planck likelihood in combination with the Bicep2/Keck/Planck (BKP) likelihood to constrain the birefringence angle $α$. Our findings, that are compatible with no detection, read $α= 0.0^{\circ} \pm 1.3^{\circ} \mbox{ (stat)} \pm 1^{\circ} \mbox{ (sys)} $ for {\sc Planck} data and $α= 0.30^{\circ} \pm 0.27^{\circ} \mbox{ (stat)} \pm 1^{\circ} \mbox{(sys)} $ for BKP data. We finally forecast the expected improvements over present constraints when the Planck BB, TB and EB spectra at high $\ell$ will be included in the analysis.