Covariant variational approach to Yang-Mills theory: Thermodynamics

The thermodynamics of SU(2) Yang-Mills theory in the covariant variational approach is studied by relating the free action density in the background of a nontrivial Polyakov loop to the pressure of the gluon plasma. The Poisson resummed expression for the pressure can be evaluated analytically in limiting cases, and shows the correct Stefan-Boltzmann limit at T -> infinity, while the limit T -> 0 is afflicted by artifacts due to massless modes in the confined phase. Several remedies to remove these artifacts are discussed. Using the numerical T = 0 solutions for the ghost and gluon propagators in the covariant variational approach as input, the pressure, energy density and interaction strength are calculated and compared to lattice data.