Large-scale alignments of quasar polarisations: a detailed study of the spinless-particle scenario

TL;DR

This study investigates quasar polarization correlations over gigaparsec scales, testing axion-photon mixing as an explanation, and concludes it is unlikely given current data, while providing new constraints on axion-like particles.

Contribution

It offers a comprehensive analysis of axion-photon mixing effects on polarization and sets new limits on axion-like particle parameters based on observational data.

Findings

Axion-photon mixing unlikely explains observed polarization correlations.

New constraints established on axion-like particle properties.

Detailed analysis of magnetic field effects on polarization.

Abstract

The main motivation for our work has been a puzzling observation concerning quasars. No one expected the existence of correlations in the polarisation of visible light coming from objects separated by gigaparsecs, until they were first reported in the form of a redshift-dependent effect that has become more and more significant with the growth of the data sample. In close connection with the observational group, we have studied in detail the most widely considered scenario, involving axion-photon mixing in extragalactic magnetic fields. After a systematic investigation, we conclude that it is very unlikely that these observations can be accounted for by axion-like particles, given current data and constraints. We also derive new limits on the parameters describing these particles. This thesis gives in particular a detailed account of the consequences of axion-photon mixing on polarisation, studies the influence of averages over the frequency (including a wave-packet treatment of the mixing), and discusses the consequences of different magnetic-field morphologies.