Euler-Heisenberg Lagrangian and photon circular polarization

TL;DR

This paper investigates how non-linear photon interactions described by the Euler-Heisenberg Lagrangian can generate circular polarization in electromagnetic radiation, with potential implications for the polarization of the Cosmic Microwave Background.

Contribution

It provides a quantum Boltzmann equation approach to compute the evolution of photon polarization states considering non-linear effects.

Findings

Derived the intensity of circular polarization from linear polarized thermal radiation.

Calculated the potential contribution to CMB circular polarization.

Solved the quantum Boltzmann equation for photon density matrix evolution.

Abstract

Considering the effective Euler-Heisenberg Lagrangian, i.e., non-linear photon-photon interactions, we study the circular polarization of electromagnetic radiation based on the time-evolution of Stokes parameters. To the leading order, we solve the Quantum Boltzmann Equation for the density matrix describing an ensemble of photons in the space of energy-momentum and polarization states, and calculate the intensity of circular polarizations. Applying these results to a linear polarized thermal radiation, we calculate the circular polarization intensity, and discuss its possible relevance to the circular polarization intensity of the Cosmic Microwave Background radiation.