Higher-order geometrical optics for electromagnetic waves on a curved
  spacetime
  We study the geometrical-optics expansion for circularly-polarized
electromagnetic waves propagating on a curved spacetime in general relativity.
We show that higher-order corrections to the Faraday and stress-energy tensors
may be found via a system of transport equations, in principle. At sub-leading
order, the stress-energy tensor possesses terms proportional to the wavelength
whose sign depends on the handedness of the circular polarization. Due to such
terms, the direction of energy flow is not aligned with the gradient of the
eikonal phase, in general, and the wave may carry a transverse stress.
