Effective Approximation of Electromagnetism for Axion Haloscope Searches

TL;DR

This paper introduces an effective approximation to Maxwell's equations incorporating axion interactions, enabling more accurate modeling of electromagnetic fields in haloscope searches, especially for complex cavity geometries and ultra-light axions.

Contribution

It presents a novel set of Maxwell's equations that inherently satisfy boundary conditions and describe axion-induced fields, improving upon previous methods in haloscope search modeling.

Findings

The new equations accurately model reacted fields in cylindrical and toroidal cavities.

A small energy difference suggests an anomalous non-dissipating current induced by axions.

The approach is effective for ultra-light axion mass regimes.

Abstract

We applied an effective approximation into Maxwell's equations with an axion interaction for haloscope searches. A set of Maxwell's equations acquired from this approximation describes just the reacted fields generated by the anomalous interaction. Unlike other approaches, this set of Maxwell's equations inherently satisfies the boundary conditions for haloscope searches. The electromagnetic field solutions from the Maxwell's equations were evaluated for both cylindrical and toroidal cavity geometries including when the axion mass becomes ultra-light (sub-meV). A small but non-zero difference between the electric and magnetic stored energies appeared in both cases. The difference may come from an anomalous non-dissipating current induced by oscillating axions.