Axion-Electromagnetic Waves

Understand

We extend the duality symmetry between the electric and the magnetic fields to the case in which an additional axion-like term is present, and we derive the set of Maxwell's equations that preserves this symmetry.

• This new set of equations allows for a gauge symmetry extending the ordinary symmetry in the classical electrodynamics.
• We obtain explicit solutions for the new set of equations in the absence of external sources, and we discuss the implications of a new internal symmetry between the axion field and the electromagnetic gauge potential.