Phase Transition in (2+1)d Quantum Gravity

(2+1) dimensional gravity is equivalent to an exactly soluble non-Abelian Chern-Simons gauge field theory (E Witten 1988). Regarding this as the topological phase of quantum gravity in (2+1)d, we suggest a topological symmetry breaking by introducing a mass term for the gauge fields, which carries a space-time metric and local dynamical degrees of freedom. We consider the finite temperature behavior of the symmetry broken phase, and claim a restoration of the topological invariance at some critical temperature. The phase transition is shown of the zeroth order.