PUB - Publikationen an der Universität Bielefeld

We discuss reorganizing finite temperature perturbation theory usinghard-thermal-loop (HTL) perturbation theory in order to improve the convergenceof successive perturbative approximations to the free energy of a gauge theory.We briefly review the history of the technique and present new results for thethree-loop HTL-improved approximation for the free energy of QED. We show thatthe hard-thermal-loop perturbation reorganization improves the convergence ofthe successive approximations to the QED free energy at intermediate coupling,e ~ 2. The reorganization is gauge invariant by construction, and due tocancellation among various contributions, one can obtain a completely analyticresult for the resummed thermodynamic potential at three loops.