Journal of Statistical Physics, Vol. 57, Nos. 3/4, 1989. p. 433-453.
A discussion is given of the role of the unstable and metastable parts (the "loop") in the equation of state of the van der Waals or Landau type for the interface theory. The role of the loop in the field-theoretic renormalization calculation of the interface is analyzed. It is shown that in real-space renor-realization no loop occurs and that a satisfactory interface calculation can be made using Migdal's renormalization procedure.