Four-loop screened perturbation theory

Understand

We study the thermodynamics of massless phi-fourth theory using screened perturbation theory.

• In this method, the perturbative expansion is reorganized by adding and subtracting a thermal mass term in the Lagrangian.
• We calculate the free energy through four loops expanding in a double power expansion in m/T and g^2, where m is the thermal mass and g is the coupling constant.
• The expansion is truncated at order g^7 and the loop expansion is shown to have better convergence properties than the weak-coupling expansion.