Renormalons in the effective potential of the vectorial   $(\vec{\varphi}^{2})^{2}$ model
  We study the properties of ultraviolet renormalons in the vectorial $(\vec{\phi}^{2})^{2}$ model. This is achieved by studying the effective potential of the theory at next to leading order of the $1/N$ expansion, the appearence ofthe renormalons in the perturbative series and their relation to the imaginary part of the potential. We also consider the mechanism of renormalon cancellation by `irrelevant" higher dimensional operators. 
L. Galli, I. Scimemi (Dip. di Fisica, Univ. "La Sapienza", Rome,   Italy)