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

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.

Comments: v2: one typo corrected. Added a few comments, matches published version