Photon-ALP interaction as a measure of initial photon polarization

Understand

Axion-like particles (ALPs) are very light, neutral, spin zero bosons predicted by superstring theory.

• ALPs interact primarily with two photons and in the presence of an external magnetic field they generate photon-ALP oscillations and the change of the polarization state of photons.
• While well motivated from a theoretical point of view, hints on ALP existence come from astrophysics.
• In this paper, we state and demonstrate some theorems about a strict relationship between initial photon polarization and photon-ALP conversion probability - which can be extrapolated by observed astrophysical spectra - so that, in the presence of ALPs, flux-measuring observatories become also porarimeters.