Cosmological Birefringence: an Astrophysical test of Fundamental Physics

Understand

We review the methods used to test for the existence of cosmological birefringence, i.e.

• a rotation of the plane of linear polarization for electromagnetic radiation traveling over cosmological distances, which might arise in a number of important contexts involving the violation of fundamental physical principles.
• The main methods use: (1) the radio polarization of radio galaxies and quasars, (2) the ultraviolet polarization of radio galaxies, and (3) the cosmic microwave background polarization.
• We discuss the main results obtained so far, the advantages and disadvantages of each method, and future prospects.