O(N) VECTOR MODEL IN THE LARGE-N LIMIT REVISITED - MULTICRITICAL POINTS AND DOUBLE SCALING LIMIT

The multicritical points of the O(N)-invariant N vector model in the l arge-RT limit are reexamined. Of particular interest are the subtletie s involved in the stability of the phase structure at critical dimensi ons. In the limit N --> infinity while the coupling g --> g(c) in a co rrelated manner (the double scaling limit) a massless bound state O(N) singlet is formed and powers of 1/N are compensated by IR singulariti es, The persistence of the N --> infinity results beyond the leading o rder is then studied with particular interest in the possible existenc e of a phase with propagating small mass vector fields and a massless singlet bound state. We point out that under certain conditions the do uble scaled theory of the singlet field is non-interacting in critical dimensions.