Nonlinear electrodynamics and CMB polarization

TL;DR

This paper investigates how nonlinear electrodynamics affects the polarization angle of CMB photons, using a specific Lagrangian model, and relates it to the universe's geometry and magnetic fields, providing constraints consistent with recent observations.

Contribution

It introduces a model linking nonlinear electrodynamics with CMB polarization, deriving polarization angle predictions based on universe geometry and magnetic field effects.

Findings

Polarization angle depends on the universe's eccentricity and magnetic fields.

Model constrains the nonlinear parameter δ using observational data.

Results are consistent with WMAP and BOOMERanG polarization constraints.

Abstract

Recently WMAP and BOOMERanG experiments have set stringent constraints on the polarization angle of photons propagating in an expanding universe: $\Delta \alpha = (-2.4 \pm 1.9)^\circ$. The polarization of the 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. For this purpose, we use the Pagels-Tomboulis (PT) Lagrangian density describing NLED, which has the form $L\sim (X/\Lambda^4)^{\delta - 1}\; X $, where $X=1/4 F_{\alpha\beta} F^{\alpha \beta}$, and $\delta$ 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.