Constraints on cosmological birefringence energy dependence from CMB
  polarization data
  We study the possibility of constraining the energy dependence of
cosmological birefringence by using CMB polarization data. We consider four
possible behaviors, characteristic of different theoretical scenarios:
energy-independent birefringence motivated by Chern-Simons interactions of the
electromagnetic field, linear energy dependence motivated by a 'Weyl'
interaction of the electromagnetic field, quadratic energy dependence,
motivated by quantum gravity modifications of low-energy electrodynamics, and
inverse quadratic dependence, motivated by Faraday rotation generated by
primordial magnetic fields. We constrain the parameters associated to each kind
of dependence and use our results to give constraints on the models mentioned.
We forecast the sensitivity that Planck data will be able to achieve in this
respect.
