Probing axion-like particles with the ultraviolet photon polarization from active galactic nuclei in radio galaxies

TL;DR

This paper uses ultraviolet polarization data from active galactic nuclei in radio galaxies to set new constraints on axion-like particles' properties, specifically their coupling to photons and the magnetic field strength.

Contribution

It provides a novel bound on the product of photon-ALP coupling and magnetic field strength using ultraviolet polarization data from radio galaxies.

Findings

Derived a new upper limit on g_{aγ} B for ultralight ALPs.

Compared the new bound with existing constraints in the literature.

Suggested potential improvements with future observations.

Abstract

The mixing of photons with axion-like particles (ALPs) in the large-scale magnetic field $B$ changes the polarization angle of a linearly polarized photon beam from active galactic nuclei in radio galaxies as it propagates over cosmological distances. Using available ultraviolet polarization data concerning these sources we derive a new bound on the product of the photon-ALP coupling $g_{a\gamma}$ times $B$. We find $g_{a\gamma} B \lesssim 10^{-11}$ GeV$^{-1}$ nG for ultralight ALPs with $m_a \lesssim 10^{-15}$ eV. We compare our new bound with the ones present in the literature and we comment about possible improvements with observations of more sources.