Circular polarisation is a very well-known prediction of synchrotron emission in Astrophysics; it is used to infer the magnetic field in astrophysical sites. Yet the emission of circularly polarised photons is also an inherent feature of (other) high energy particle physics processes, that are independent of the local magnetic field. I will discuss how we can use this effect to constrain the nature of dark matter, the existence of sterile neutrinos and probe a neutrino asymmetry in astrophysical sites.
