AN OPERATOR FORMALISM FOR UNITARY MATRIX MODELS
Konstantinos N Anagnostopoulos, Mark J. Bowick, Nobuyuki Ishibashi · Modern Physics Letters A · 1991
We analyze the double scaling limit of unitary matrix models in terms of trigonometric orthogonal polynomials on the circle. In particular we find a compact formulation of the string equation at the kth multicritical point in terms of pseudodifferential operators and a corresponding action principle. We also relate this approach to the mKdV hierarchy which appears in the analysis in terms of conventional orthogonal polynomials on the circle.