PUB - Publikationen an der Universität Bielefeld

A Feynman-Jensen version of the thermal variational principle is applied tohot gauge fields, Abelian as well as non-Abelian: scalar electrodynamics(without scalar self-coupling) and the gluon plasma. The perturbatively knownself-energies are shown to derive by variation from a free quadratic(''Gaussian'') trial Lagrangian. Independence of the covariant gauge fixingparameter is reached (within the order $g^3$ studied) after a reformulation ofthe partition function such that it depends on only even powers of the gaugefield. Also static properties (Debye screening) are reproduced this way. Butbecause of the present need to expand the variational functional, the methodfalls short of its potential nonperturbative power.