Vortices and the non-singlet sector of the c = 1 matrix model

The role of the non-singlet sector of the matrix model representation of c = 1 matter coupled to two-dimensional quantum gravity is studied in the case where the target space is a circle of finite radius. It is argued that this sector decouples for large enough radius, since the non-singlet state energies are logarithmically divergent in the double scaling limit that reproduces continuum surfaces. We identify the degrees of freedom described by this sector as vortices on the world-sheet, which are dynamically irrelevant for large radius (low temperature) but condense at a critical value of the radius, giving rise to a Kosterlitz-Thouless phase transition.