We develop a method to constrain non-isotropic features of Cosmic Microwave Background (CMB) polarization, of a type expected to arise in some models describing quantum gravity effects on light propagation. We describe the expected signatures of this kind of anomalous light propagation on CMB photons, showing that it will produce a non-isotropic birefringence effect, i.e. a rotation of the CMB polarization direction whose observed amount depends in a peculiar way on the observation direction. We also show that the sensitivity levels expected for CMB polarization studies by the \emph{Planck} satellite are sufficient for testing these effects if, as assumed in the quantum-gravity literature, their magnitude is set by the minute Planck length.
@article{arxiv.1106.6049,
title = {Using CMB data to constrain non-isotropic Planck-scale modifications to Electrodynamics},
author = {Giulia Gubitosi and Marina Migliaccio and Luca Pagano and Giovanni Amelino-Camelia and Alessandro Melchiorri and Paolo Natoli and Gianluca Polenta},
journal= {arXiv preprint arXiv:1106.6049},
year = {2015}
}