Wide-band full-wave electromagnetic modal analysis of the coupling between dark-matter axions and photons in microwave resonators

TL;DR

This paper introduces a comprehensive full-wave modal analysis method using BI-RME to study axion-photon coupling in microwave resonators, enabling broad-band, phase-aware detection of axion-induced electromagnetic signals.

Contribution

The work develops a novel 3D boundary integral-resonant mode expansion technique for analyzing axion-photon interactions in microwave cavities, accounting for arbitrary axion field variations.

Findings

Able to calculate RF power spectrum without approximations

Provides full knowledge of signal magnitude and phase

Handles modes close to the axion resonance

Abstract

The electromagnetic coupling axion-photon in a microwave cavity is revisited with the Boundary Integral - Resonant Mode Expansion (BI-RME) 3D technique. Such full-wave modal technique has been applied for the rigorous analysis of the excitation of a microwave cavity with an axion field. In this scenario, the electromagnetic field generated by the axion-photon coupling can be assumed to be driven by equivalent electrical charge and current densities. These densities have been inserted in the general BI-RME 3D equations, which express the RF electromagnetic field existing within a cavity as an integral involving the Dyadic Green functions of the cavity (under Coulomb gauge) as well as such densities. This method is able to take into account any arbitrary spatial and temporal variation of both magnitude and phase of the axion field. Next, we have obtained a simple network driven by the axion current source, which represents the coupling between the axion field and the resonant modes of the cavity. With this approach, it is possible to calculate the extracted and dissipated RF power as a function of frequency along a broad band and without Cauchy-Lorentz approximations, obtaining the spectrum of the electromagnetic field generated in the cavity, and dealing with modes relatively close to the axion resonant mode. Moreover, with this technique we have a complete knowledge of the signal extracted from the cavity, not only in magnitude but also in phase. This can be an interesting issue for future analysis where the axion phase is an important parameter.