Modified axion electrodynamics as impressed electromagnetic sources through oscillating background polarization and magnetization

Abstract

A reformulation of axion modified electrodynamics is presented where the equations maintain a similar form to the unmodified Maxwell's equations, with all modifications redefined within the constitutive relations between the D, H, B and E fields. This allows the interpretation of the axion induced background bound charge, polarization current and bound current along with the axion induced polarization and magnetization with the former satisfying the charge-current continuity equation. This representation is of similar form to odd-parity Lorentz invariance violating background fields in the photon sector of the Standard Model Extension. We show that when a DC B-field is applied an oscillating background polarization is induced at a frequency equivalent to the axion mass. In contrast, when a large DC E-field is applied, an oscillating background magnetization is induced at a frequency equivalent to the axion mass. It is evident that these terms are equivalent to impressed source terms, analogous to the way that voltage and current sources are impressed into Maxwell's equations in circuit and antenna theory. The impressed source terms represent the conversion of external energy into electromagnetic energy due to the inverse Primakoff effect converting energy from axions into oscillating electromagnetic fields. It is shown that the impressed electrical DC current that drives a DC magnetic field of an electromagnet, induces an impressed effective magnetic current (or voltage source) parallel to the DC electrical current oscillating at the Compton frequency of the axion. The effective magnetic current drives a voltage source through an electric vector potential and also defines the boundary condition of the oscillating axion induced polarization (or impressed axion induced electric field) inside and outside the electromagnet. This impressed electric field, like in any voltage source, represents an extra force per unit charge supplied to the system, which also adds to the Lorentz force.

Electromagnetism, axions, and topology: A first-order operator approach to constitutive responses provides greater freedom

“…i.e. satisfying (4), (5). Imposing this, we show in appendix B that this reduces the number of "physical" components of 16.…”

“…It is important to note that whatever other dynamical equations that these auxiliary fields (Ě,B) might follow, they cannot be the same as the standard Maxwellian (4), (5). Note that here the sourcesρ andJ might be the ordinary charge and current ρ and J , and not new types of sources.…”

“…As an example, we can model a medium with an axionic response together with a simple constant permittivity ε and permeability µ as per (4), (5), and so replace (6), (7), (9) for this type of medium with the relations…”

“…We also suggest an experimental scenario where such an axionic field can be emulated. Although a discussion of axions in the context of EM is an established area of research [5,6], this usually occurs in the context of an added coupling between the Maxwell fields and the field of an axion particle. This * https://orcid.org/0000-0003-1597-6084 † https://orcid.org/0000-0003-0643-7169 ‡ https://orcid.org/0000-0001-5744-8146 contrasts with our axionic response terms, which result from a constitutive property of the background medium.…”

“…This * https://orcid.org/0000-0003-1597-6084 † https://orcid.org/0000-0003-0643-7169 ‡ https://orcid.org/0000-0001-5744-8146 contrasts with our axionic response terms, which result from a constitutive property of the background medium. Notably, the Lagrangian for coupling EM to a particle physics type axion field (Ξ) has the form [5,6]…”