Boundary and interface effects in Carrollian axion electrodynamics

Determine whether boundaries or interfaces between media can alter the phase-space structure and generate physical effects, including a nonzero magnetoelectric response, in Carrollian axion electrodynamics.

Background

The bulk magnetic Carroll axion theory has no linear magnetoelectric effect because its reduced free energy depends only on static axion configurations and the physical Hamiltonian is independent of the canonical momentum associated with the effective electric field.

The authors leave unresolved whether boundaries, interfaces, and their associated boundary conditions can change the constrained phase-space structure and thereby produce physics absent in the bulk. They also point to spatially varying axion configurations as a possible source of additional effects.