No chiral light bending by clumps of axion-like particles

Understand

We study the propagation of light in the presence of a parity-violating coupling between photons and axion-like particles (ALPs).

• Naively, this interaction could lead to a split of light rays into two separate beams of different polarization chirality and with different refraction angles.
• However, by using the eikonal method we explicitly show that this is not the case and that ALP clumps do not produce any spatial birefringence.
• This happens due to non-trivial variations of the photon's frequency and wavevector, which absorb time-derivatives and gradients of the ALP field.