Screened perturbation theory at four loops Original Research Article

We study the thermodynamics of massless ϕ4-theory using screened perturbation theory, which is a way to systematically reorganise the perturbative series. The free energy and pressure are calculated through four loops in a double expansion in powers of g2 and m/T, where m is a thermal mass of order gT. The result is truncated at order g7. We find that the convergence properties are significantly improved compared to the weak-coupling expansion.