Nordita Astrophysics Seminars

Axion-photon conversion in neutron star magnetospheres

by Dr Alexander J. Millar (OKC, Stockholm University; Nordita)

Europe/Stockholm
https://stockholmuniversity.zoom.us/j/530682073

https://stockholmuniversity.zoom.us/j/530682073

Description

Axion dark matter can resonantly convert to photons in the magnetosphere of neutron stars, possibly giving rise to radio signals observable on Earth. This method for the indirect detection of axion dark matter has recently received significant attention in the literature, which I will review in this talk. The calculation of the radio signal is complicated by a number of effects; most importantly, the gravitational infall of the axions onto the neutron star accelerates them to semi-relativistic speed, and the neutron star magnetosphere is highly anisotropic. Both of these factors complicate the calculation of the conversion of axions to photons. In this work, we present the first fully three-dimensional calculation of the axion-photon conversion in highly magnetised anisotropic media. Depending on the axion trajectory, this calculation leads to orders-of-magnitude differences in the conversion compared to the simplified one-dimensional calculation used so far in the literature, altering the directionality of the produced photons.