Effective Lagrangians in 2 (+epsilon) dimensions - art. no. 076001

The failure of the the loop expansion and effective Lagrangians in two dime nsions, which traditionally hinges on a power counting argument, is conside red. We establish that, subject to certain restrictions, the pion-decay con stant, which is a bookkeeping device for the loop expansion, vanishes for d = 2, thereby taking us beyond the power counting argument. We point out th e connection of our results to the distinct phases of the candidate for the effective Lagrangians, the nonlinear sigma model. in d = 2 + epsilon, and eventually for d = 2. In light of our results, we recall some of the releva nt features of the multiflavor Schwinger and large N-f QCD(2) as candidates for the underlying theory in d = 2.