  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
$\alpha$. Our findings, that are compatible with no detection, read $\alpha =
0.0^{\circ} \pm 1.3^{\circ} \mbox{ (stat)} \pm 1^{\circ} \mbox{ (sys)} $ for
{\sc Planck} data and $\alpha = 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.
