Exact spectra of conformal supersymmetric nonlinear sigma models in two dimensions

We study two-dimensional nonlinear sigma models in which the target spaces are the coset supermanifolds U(n + m \n)/[U(1) x U(n + m - 1 \n)] congruent to CPn+m-1 \n (projective superspaces) and OSp(2n + m \ 2n)/OSp(2n + m - 1 \ 2n) congruent to S2n+m-1 \ 2n (superspheres), n, m integers, -2 less tha n or equal to m less than or equal to 2; these quantum field theories live in Hilbert spaces with indefinite inner products. These theories possess no n-trivial con formally-invariant renormalization-group fixed points, or in some cases, lines of fixed points. Some of the conformal fixed-point theori es can also be obtained within Landau-Ginzburg theories. We obtain the comp lete spectra (with multiplicities) of exact conformal weights of states (or corresponding local operators) in the isolated fixed-point conformal field theories, and at one special point on each of the lines of fixed points. A lthough the conformal weights are rational, the conformal field theories ar e not, and (with one exception) do not contain the affine versions of their superalgebras in their chiral algebras. The method involves lattice models that represent tl e strong-coupling region, which can be mapped to loop mo dels, and then to a Coulomb gas with modified boundary conditions. The resu lts apply to percolation, dilute and dense polymers, and other statistical mechanics models, and also to the spin quantum Hall transition in non-inter acting fermions with quenched disorder. (C) 2001 Published by Elsevier Scie nce B.V.