Axion-like particles and circular polarisation of active galactic nuclei

Abstract

The measurements of the linear polarisation of visible light from quasars give strong evidence for large-scale coherent orientations of their polarisation vectors in some regions of the sky. We show that these observations can be explained by the mixing of the photons with very light pseudoscalar (axion-like) particles in extragalactic magnetic fields during their propagation. We present a new treatment in terms of wave packets and discuss the circular polarisation.

Contributed to the "5th Patras Workshop on Axions, WIMPs and WISPs", Durham 13-17 July 2009