POLARIZATION OF A QED PLASMA IN A STRONG MAGNETIC-FIELD

In this paper we study the polarization tenser of photons in a QED pla sma in the presence of a magnetic field. We do it both at vanishing an d at finite temperature. We use two different methods to compute the p olarization tenser components IImu nu within the one-loop approximatio n. The first starts from the effective Lagrangian of the system and re lates IImu nu to the thermodynamic quantities. The second makes use of the electron propagator in an external magnetic field. In this second approach we use an imaginary time formalism. These methods give consi stent results in the first nonvanishing order in the photon four-momen tum. Beyond this limit the first method is not applicable and the intr oduction of the second cannot be avoided. We give some physical interp retations of our results.