Simulating Axion Electrodynamics in Magnetized Plasmas: Energy transfer in the inhomogeneous and strongly varying limit

Abstract

In this work we study the electromagnetic response induced by axions in a magnetized plasma, focusing specifically on characterizing energy transfer and energy losses from the ambient axion field in highly inhomogeneous and strongly varying backgrounds. Using a suite of both frequency-domain and time-domain simulations, we solve for: the efficiency of photon excitation in a rapidly varying background, the indirect excitation of Alfv\'en modes, occurring when a Langmuir-Ordinary (LO) mode is resonantly excited near a combined cutoff-resonance of the dispersion relations of the LO and Alfv\'en modes, and the excitation of electric fields in small localized plasma under-densities. We identify a particularly interesting regime in which energy can be transferred into sub-luminal plasma modes ($\omega < k$) with an efficiency greater than that of super-luminal modes ($\omega > k$). Our results highlight a variety of less conventional ways in which axions (and other light degrees of freedom that mix with electromagnetism, such as dark photons or gravitons) can interact in extreme astrophysical environments.