On the circular polarisation of light from axion-photon mixing
  From the analysis of measurements of the linear polarisation of visible light
coming from quasars, the existence of large-scale coherent orientations of
quasar polarisation vectors in some regions of the sky has been reported. Here,
we show that this can be explained by the mixing of the incoming photons with
nearly massless pseudoscalar (axion-like) particles in extragalactic magnetic
fields. We present a new treatment in terms of wave packets and discuss its
implications for the circular polarisation.
