ALP-photon Mixing in Pulsar Magnetospheres

Some extensions of the Standard Model suggest the existence of light, pseudo-scalar particles such as axions or axion-like particles (ALPs). Such particles couple to photons in the presence of an external magnetic field. As a result of this coupling ALP-photon oscillations will affect the propagation of very-high-energy gamma rays in strong magnetic field environments, as in the case of magnetosphere of pulsars. The emission regions of very-high-energy photons from pulsars are thought to be limited by the opacity of the magnetosphere due to the strong magnetic fields present. ALP-photon mixing in the inner pulsar magnetosphere allows for ALPs to propagate unimpeded by pair attenuation leading to an observable modification to the pulsar light-curve. We simulated the propagation of very-high-energy photons through a pulsar magnetosphere where ALP-photon mixing is present. For a range of ALP parameters and magnetic field strengths, ALP-photon mixing is shown to alter the opacity of pulsar magnetospheres to very-high-energy photons.