Using CMB data to constrain non-isotropic Planck-scale modifications to Electrodynamics

TL;DR

This paper proposes a method to detect non-isotropic quantum gravity effects on light using CMB polarization data, focusing on birefringence signatures that vary with observation direction, and assesses Planck satellite sensitivity for such tests.

Contribution

It introduces a novel approach to constrain non-isotropic Planck-scale modifications to electrodynamics through CMB polarization analysis.

Findings

Planck data can test quantum gravity-induced birefringence effects.

Non-isotropic birefringence produces direction-dependent polarization rotation.

Sensitivity levels are sufficient to detect effects if they are set by the Planck length.

Abstract

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.