Thermal effects and the effective action of quantum electrodynamics

We study the influence of temperature on the nonlinear effective action of QED, in the presence of constant external fields, by means of the Fock-Schwinger proper time method. The analysis is done according to thermo field dynamics. This is an extension of the work done by Dittrich and we comment on the case of a constant electric field. In this way we find an effective thermal Euler-Heisenberg Lagrangian, identifying the effective thermal coupling constant and an effective thermal mass for the photon. © 1992 The American Physical Society.