Nonlocality in (1/N)-expanded nonrenormalizable interactions

Nonrenormalizable interactions are studied on the example of the (1/N)PHI46 model with interaction via the collective chi = PHI2 mode. In 4<d<6 dimensions, the model is nonrenormalizable by power counting but it does not require more subtractions than in the four-dimensional case. In six dimensions, nonrenormalizability is essential: There are two induced couplings chi3 and chi.f(chi). The chi3 coupling strength can be determined from the requirement that the effective potential has a minimum at PHI2=chi=0. The nonlocal formfactor produced by an infinite number of chi.f(chi) insertions cannot be determined uniquely, however the ambiguity concentrates in the leading order only. This formfactor is constructed using the method of Efimov and Mogilevsky. The resulting theory satisfies unitarity, microcausality and correct spectral properties. (Auth.)