## Sigma models with A_k singularities in Euclidean spacetime of dimension 0<=D<4 and in the limit N->infinity

• For the case of the single-O(N)-vector linear sigma models the critical behaviour following from any A_k singularity in the action is worked out in the double scaling limit N->infinity, f_r -> f_r^c, 2 <= r <= k. After an exact elimination of Gaussian degrees of freedom, the critical objects such as coupling constants, indices and susceptibility matrix are derived for all A_k and spacetime dimensions 0 <= D <= 4. There appear exceptional spacetime dimensions where the degree k of the singularity A_k is more strongly constrained than by the renormalizability requirement.

$Rev: 13581$