Cornering the axion-like particle explanation of quasar polarisations

TL;DR

This paper critically examines the axion-like particle hypothesis for quasar polarisation alignments, arguing that recent radio polarisation data challenge the necessity of such particles as an explanation.

Contribution

It highlights how recent radio polarisation observations weaken the case for axion-like particles causing quasar polarisation alignments.

Findings

Radio polarisation data disfavor axion-like particle explanations.

Circular polarisation measurements are inconsistent with axion-induced effects.

Large-scale polarisation alignments are unlikely due to axion-like particles.

Abstract

In a series of paper, it has been shown that the distribution of polarisation position angles for visible light from quasars is not random in extremely large regions of the sky. As explained in a recent article, the measurement of vanishing circular polarisation for such quasars is an important problem for a mechanism involving the mixing with axion-like particles in external magnetic fields. In this note, we stress that a recent report of similar coherent orientations of polarisation in radiowaves further disfavours the need for such particles, as an effect at these wavelengths would be extremely suppressed or would directly contradict data.