Two-loop effective potential in noncommutative scalar field theory
  The renormalization of effective potential for the noncommutative scalar field theory is investigated to the two-loop approximation. It is seen that the nonplanar diagram does not appear in the one-loop potential. However, nonplanar diagram can become dominant in the two-loop level as the noncommutativity of geometry is sufficiently small. The result shows that the radiative corrections from the nonplanar diagrams have an inclination to induce the spontaneously symmetry breaking if it is not broken in the tree level, and have an inclination to restore the symmetry breaking if it has been broken in the tree level. 
Wung-Hong Huang