Axions and X-ray polarimetry.

Axions are one of the best motivated extensions to the Standard Model, both solving the strong CP problem and providing a natural dark matter candidate.
X-Ray telescope observations have already placed world leading bounds on the axion-photon coupling by searching for axion-photon interconversion in the magnetic fields of galaxy clusters. However, current X-ray telescopes are unable to exploit one of the most striking features of this effect: only photons polarised parallel to the background magnetic field mix with axions. This leads to distinctive polarisation signatures from astrophysical sources. The next generation of polarising X-ray telescopes could detect these signatures. I will discuss the opportunities and difficulties of detecting axions with X-ray polarimetry.