Large-scale coherent orientations of quasar polarisation vectors:
  interpretation in terms of axion-like particles
  The observation of redshift-dependent coherent orientations of quasar
polarisation vectors over cosmological distances in some regions of the sky is
reviewed. Based on a good-quality sample of 355 measured quasars, this
observation seems to infer the existence of a new effect acting on light
propagation on such huge distances. A solution in terms of nearly massless
axion-like particles has been proposed in the literature and its current status
is discussed.
