We study the phase transition properties of the nonlinear O(N) σ model in two dimensions when O(N) gauge interactions are included. With nonzero gauge coupling, this theory exhibits a first-order phase transition in the large-N limit. The broken-symmetry phase is stabilized by the Higgs mechanism and Goldstone bosons do not appear. © 1976 The American Physical Society.

At large N, the 6 theory is shown to possess a nontrivial ultraviolet fixed point. A new phase is found where asymptotic scale invariance is spontaneously broken and a dynamical mass is generated through dimensional transmutation. At the tricritical limit, the spontaneous breaking of an exact scale invariance at leading N results in the formation of a massless composite Goldstone mode, the dilaton. We compare these results to standard 1N expansion and emphasize the nonperturbative nature of these phenomena. © 1984 The American Physical Society.