Thermal Gauge Field Theories

The real- and imaginary-time-formalisms of thermal field theory and their extension to gauge theories is reviewed. Questions of gauge (in-)dependence are discussed in detail, in particular the possible gauge dependences of the singularities of dressed propagators from which the quasiparticle spectrum is obtained. The existing results on next-to-leading order corrections to non-Abelian screening and dispersion laws of hard-thermal-loop quasiparticles are surveyed. Finally, the role of the asymptotic thermal masses in self-consistent approximations to thermodynamic potentials is described and it is shown how the problem of the apparently poor convergence of thermal perturbation theory might be overcome.