  The axion photon system in an external magnetic field, when for example
considered with the geometry of the experiments exploring axion photon mixing
(which can be represented by a 1+1 effective model) displays a continuous
axion-photon duality symmetry in the limit the axion mass is neglected. The
conservation law that follows from this symmetry is obtained. The magnetic
field interaction is seen to be equivalent to first order to the interaction of
a complex charged field with an external electric potential, where this
ficticious "electric potential" is proportional to the external magnetic field.
This allows one to solve for the scattering amplitudes using already known
scalar QED results. Axion photon oscillations can be understood as violations
of a charge symmetry in the scalar QED language. Going beyond the linear
theory, the axion photon system in a self consistent magnetic field is shown,
using this formalism, to have interesting soliton solutions that represent new
non gravitational ways of trapping light. Finally, generalizing the scalar QED
formalism to 2+1 dimensions makes it clear that a photon and an axion splitt
into two components in an inhomogeneous magnetic field, an effect that reminds
us of the Stern Gerlach experiment.
