Renormalization conditions and the effective potential of the massless   phi^4 theory
  We point out that there is a missing portion in the two-loop effective potential of the massless O(N) phi^4 theory obtained by Jackiw in his classic paper, Phys. Rev. D 9, 1686 (1974). 
J. -M. Chung and B. K. Chung (Kyung Hee Univ.)