Nonlinear electrodynamics and CMB polarization

The polarization of Cosmic Microwave Background radiation (CMB) is reviewed in the context of nonlinear electrodynamics (NLED). We compute the polarization angle of photons propagating in a cosmological background with planar symmetry. The Lagrangian density describing the Pagels-Tomboulis (PT) nonlinear electrodynamics has the form L~X, where X = FF, and the parameter featuring the non-Maxwellian character of the PT nonlinear description of the electromagnetic interaction. After looking at the polarization components in the plane orthogonal to the (x)-direction of propagation of the CMB photons, the polarization angle is defined in terms of the eccentricity of the universe, a geometrical property whose evolution on cosmic time (from the last scattering surface to the present) is constrained by the strength of magnetic fields over extragalactic distances. Then, by making use of recent data on CMB polarization from WMAP and BOOMERanG, we infer the constraints on the parameter characterizing the nonlinearity of electrodynamics alla PT