Phase structure of four-dimensional simplicial quantum gravity with a U(1)gauge field

The phase structure of four-dimensional simplicial quantum gravity coupled to a U(1) gauge field is investigated numerically with the dynamical triang ulation method. A smooth phase is found in the region between the crumpled phase and the branched polymer phase. This new phase has a negative string susceptibility exponent. The phase transition between the smooth phase and the crumpled phase is studied using the finite size scaling method. Rom the numerical results we conclude that this model has a phase transition that is higher than first-order. Numerical results suggest a possibility of the existence of the continuum limit at the critical point.