GENERALIZED KAZAKOV-MIGDAL-KONTSEVICH MODEL - GROUP-THEORY ASPECTS

The Kazakov-Migdal model, if considered as a functional of external fields, can always be represented as an expansion over characters of the GL group. The integration over ''matter fields'' can be interpreted as going over the model (the space of all highest weight representations) of GL. In the case of compact unitary groups the integrals should be substituted by discrete sums over the weight lattice. The D = 0 version of the model is the generalized Kontsevich integral, which in the above-mentioned unitary (discrete) situation coincides with the partition function of 2D Yang-Mills theory with the target space of genus 0 = 0 and m = 0, 1, 2 holes. This particular quantity is always a bilinear combination of characters and appears to be a Toda lattice tau function. (This is a generalization of the classical statement that individual GL characters are always singular KP tau functions.) The corresponding element of the universal Grassmannian is very simple and somewhat similar to the one arising in investigations of the c = 1 string models. However, in certain circumstances the formal sum over representations should be evaluated by the steepest descent method, and this procedure leads to some more-complicated elements of the Grassmannian. This ''Kontsevich phase,'' as opposed to the simple ''character phase,'' deserves further investigation.