Large-scale coherent orientations of quasar polarisation vectors: interpretation in terms of axion-like particles

TL;DR

This paper reviews the observation of large-scale, redshift-dependent quasar polarisation alignments and discusses their possible explanation via axion-like particles affecting light over cosmological distances.

Contribution

It presents a comprehensive review of quasar polarisation alignments and explores the potential role of axion-like particles as a novel explanation for this phenomenon.

Findings

Observation of coherent polarisation orientations over large scales

Possible link to axion-like particles affecting light propagation

Implication for new physics beyond standard models

Abstract

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.