Mass expansions of screened perturbation theory - art. no. 105012

The thermodynamics of massless phi (4) theory is studied within screened pe rturbation theory (SPT). In this method the perturbative expansion is reorg anized by adding and subtracting a mass term in the Lagrangian. We analytic ally calculate the pressure and entropy to three-loop order and the screeni ng mass to two-loop order, expanding in powers of m/T. The truncated m/T ex pansion results are compared with numerical SPT results for the pressure, e ntropy and screening mass which are accurate to all orders in m/T. It is sh own that the m/T expansion converges quickly and provides an accurate descr iption of the thermodynamic functions for large values of the coupling cons tant.