No chiral light bending by clumps of axion-like particles

TL;DR

This paper demonstrates that axion-like particle clumps do not cause light birefringence, challenging naive expectations, and suggests new methods for probing ALP-photon interactions through frequency measurements.

Contribution

The study provides a detailed analysis showing that ALP clumps do not induce spatial birefringence in light, clarifying the effects of parity-violating couplings.

Findings

ALP clumps do not produce spatial birefringence in light.

Frequency and wavevector variations absorb ALP field gradients.

Proposes using frequency measurements to probe ALP-photon couplings.

Abstract

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. We argue that these variations represent a new way to probe the ALP-photon couping with precision frequency measurements.