The 2-Loop Effective Potential of the 3d SU(2)-Higgs Model in a General   Covariant Gauge
  To study the convergence of the loop expansion at the high-temperature electroweak phase transition, we calculate the 2-loop effective potential of the 3d SU(2)-Higgs model in a general covariant gauge. We find that the loop expansion definitely breaks down for large $\xi$, but converges rather well for smaller values, deep in the broken phase. 
M.Laine