Gauged nonlinear sigma model and boundary diffeomorphism algebra

We consider Chern-Simons gauged nonlinear sigma model with boundary which h as a manifest bulk diffeomorphism invariance. We find that the Gauss's law can be solved explicitly when the nonlinear sigma model is defined on the H ermitian symmetric space, and the original bulk theory completely reduces t o a boundary nonlinear sigma model with the target space of Hermitian symme tric space. We also study the symplectic structure, compute the diffeomorph ism algebra on the boundary, and find an (enlarged) Virasoro algebra with c lassical central term. (C) 1999 Published by Elsevier Science B.V. All righ ts reserved.