Cosmological Birefringence and the Geometric Phase of Photons
  Regarding axion electrodynamics in the background flat FRW universe, we show
that cosmological birefringence arises from an adiabatic noncyclic geometric
phase that appears in the quantum state of photons because of their interaction
with the axion field. We also show that the axion electrodynamics is equivalent
to standard electrodynamics in time-dependent bi-isotropic magnetoelectric
Tellegen media, which serves as an analogue system that can simulate
cosmological birefringence.
