Axion-photon Propagation in Magnetized Universe

Understand

Oscillations between photons and axion-like particles (ALP) travelling in intergalactic magnetic fields have been invoked to explain a number of astrophysical phenomena, or used to constrain ALP properties using observations.

• One example is the anomalous transparency of the universe to TeV gamma-rays.
• The intergalactic magnetic field is usually modeled as patches of coherent domains, each with a uniform magnetic field, but the field orientation changes randomly from one domain to the next ("discrete-$\varphi$ model").
• We show in this paper that in more realistic situations, when the magnetic field direction varies continuously along the propagation path, the photon-to-ALP conversion probability $P$ can be significantly different from the discrete-$\varphi$ model.