QED effective action at finite temperature

The QED effective Lagrangian in the presence of an arbitrary constant electromagnetic background field at finite temperature is derived in the imaginary-time formalism to one-loop order. The boundary conditions in imaginary time reduce the set of gauge transformations of the background field, which allows for a further gauge invariant and puts restrictions on the choice of gauge. The additional invariant enters the effective action by a topological mechanism and can be identified with a chemical potential; it is furthermore related to Debye screening. In concordance with the real-time formalism, we do not find a thermal correction to Schwinger's pair-production formula. The calculation is performed on a maximally Lorentz covariant and gauge invariant stage.Comment: 9 pages, REVTeX, 1 figure, typos corrected, references added, final version to appear in Phys. Rev.

Light Cone Condition for a Thermalized QED Vacuum

Within the QED effective action approach, we study the propagation of low-frequency light at finite temperature. Starting from a general effective Lagrangian for slowly varying fields whose structure is solely dictated by Lorentz covariance and gauge invariance, we derive the light cone condition for light propagating in a thermalized QED vacuum. As an application, we calculate the velocity shifts, i.e., refractive indices of the vacuum, induced by thermalized fermions to one loop. We investigate various temperature domains and also include a background magnetic field. While low-temperature effects to one loop are exponentially damped by the electron mass, there exists a maximum velocity shift of $-\delta v^2_{max}=\alpha/(3\pi)$ in the intermediate-temperature domain $T\sim m$.Comment: 9 pages, 3 figures, REVTeX, typos corrected, final version to appear in Phys. Rev.

Generalizations of the thermal Bogoliubov transformation

The thermal Bogoliubov transformation in thermo field dynamics is generalized in two respects. First, a generalization of the $\alpha$--degree of freedom to tilde non--conserving representations is considered. Secondly, the usual $2\times2$ Bogoliubov matrix is extended to a $4\times4$ matrix including mixing of modes with non--trivial multiparticle correlations. The analysis is carried out for both bosons and fermions.Comment: 20 pages, Latex, Nordita 93/33

QED Effective Action at Finite Temperature: Two-Loop Dominance

We calculate the two-loop effective action of QED for arbitrary constant electromagnetic fields at finite temperature T in the limit of T much smaller than the electron mass. It is shown that in this regime the two-loop contribution always exceeds the influence of the one-loop part due to the thermal excitation of the internal photon. As an application, we study light propagation and photon splitting in the presence of a magnetic background field at low temperature. We furthermore discover a thermally induced contribution to pair production in electric fields.Comment: 34 pages, 4 figures, LaTe

Neutrino self-energy and dispersion in a medium with magnetic field

We calculate the one-loop thermal self-energy of a neutrino in a constant and homogeneous magnetic field to all orders in the magnetic field strength using Schwinger's proper time method. We obtain the dispersion relation under various conditions.Comment: 17 pp, RevTeX, one figur

THERMAL EFFECTS ON THE CATALYSIS BY A MAGNETIC FIELD

We show that the formation of condensates in the presence of a constant magnetic field in 2+1 dimensions is extremely unstable. It disappears as soon as a heat bath is introduced with or without a chemical potential. We point out some new nonanalytic behavior that develops in this system at finite temperature.Comment: 10 pages, plain Te

Effective Electromagnetic Lagrangian at Finite Temperature and Density in the Electroweak Model

Using the exact propagators in a constant magnetic field, the effective electromagnetic Lagrangian at finite temperature and density is calculated to all orders in the field strength B within the framework of the complete electroweak model, in the weak coupling limit. The partition function and free energy are obtained explicitly and the finite temperature effective coupling is derived in closed form. Some implications of this result, potentially interesting to astrophysics and cosmology, are discussed.Comment: 14 pages, Revtex