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In this work we examine refraction of light by computing full solutions to axion electrodynamics. We also allow for the possibility of an additional plasma component. We then specialise to wavelengths which are small compared to background scales to determine if refraction can be described by geometric optics. We also allow for the possibility of an additional plasma component. In the absence of plasma, for small incidence angles relative to the optical axis, axion electrodynamics and geometric optics are in good agreement, with refraction occurring at $mathcal{O}(g_{a gamma gamma}^2)$. However, for rays which lie far from the optical axis, the agreement with geometric optics breaks down and the dominant refraction requires a full wave-optical treatment, occurring at $mathcal{O}(g_{a gamma gamma})$. In the presence of sufficiently large plasma masses, the wave-like nature of light becomes suppressed and geometric optics is in good agreement with the full theory for all rays. Our results therefore suggest the necessity of a more comprehensive study of lensing and ray-tracing in axion backgrounds, including a full account of the novel $mathcal{O}(g_{a gamma gamma})$ wave-optical contribution to refraction.
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 chiralit
The decay of a massive pseudoscalar, scalar and U(1) boson into an electron-positron pair in the presence of strong electromagnetic backgrounds is calculated. Of particular interest is the constant-crossed-field limit, relevant for experiments that a
We attempt to identify a phenomenologically viable solution to the strong $CP$ problem in which the axion is composed entirely out of Standard Model fermion species. The axion consists predominantly of the $eta$ meson with a minuscule admixture of a
We use AdS/CFT to construct the gravitational dual of a 5D CFT in the background of a non-extremal rotating black hole. Our boundary conditions are such that the vacuum state of the dual CFT corresponds to the Unruh state. We extract the expectation
The QCD axion mass may receive contributions from small-size instantons or other Peccei-Quinn breaking effects. We show that it is possible for such a heavy QCD axion to induce slow-roll inflation if the potential is sufficiently flat near its maximu