The dynamical triangulation model of three-dimensional quantum gravity is shown to have a line of transitions in an expanded phase diagram which includes a coupling µ to the order of the vertices. Monte Carlo renormalization group and finite size scaling techniques are used to locate and characterize this line. Our results indicate that for µ < µ1 ∼ −1.0 the model is always in a crumpled phase independent of the value of the curvature coupling. For µ < 0 the results are in agreement with an approximate mean field treatment. We find evidence that this line corresponds to first order transitions extending to positive µ. However the behavior appears to change for µ > µ2 ∼ 2.0 − 4.0. The simplest scenario that is consistent with the data is the existence of a critical end point.PACS numbers: 04.60.+n, 05.70.Jk, 11.10.Gh
I. DYNAMICAL TRIANGULATIONS WITH A MEASURE TERMTriangulations provide a discretization of curved Euclidean spacetimes. In the Regge approach, a specific simplicial lattice is chosen a priori and the properties of the spacetime are determined by the length of the lattice links. A complementary approach, dynamical triangulations, fixes the length of the links to an invariant cut-off and allows the lattice connectivity to determine the geometry of the spacetime. This paper uses the latter approach. A lattice representation of the Einstein-Hilbert action iswhere N 0 is the number of vertices and N D the number of simplices in the triangulation (the latter is then also the volume), D is the dimension of the system and α and β are corresponding chemical potentials. The coupling β serves as the cosmological constant while α is related to Newton's gravitational constant. The connectivity of a triangulation plays the same role as the metric in continuous manifolds in the sense that points joined by a link are considered close together while those not connected are considered further apart. Continuum theories of quantum gravity generally involve an integration over all possible physically inequivalent metrics. In dynamical triangulation models, a sum over triangulations (i.e a sum over all allowed connectivities) fulfills the same need. Consequently, the partition function for the dynamical triangulation model of quantum gravity iswhere the sum is over all possible triangulations with fixed topology, S is the action given above and the term ρ(T ) allows for the possibility of a non-trivial measure in the space of triangulations. Matter can be coupled to the gravity by adding appropriate terms to eqn. (1) and including a sum over the matter degrees of freedom in eqn.(2). These models of quantum gravity have proven themselves in two dimensions where analytical results are available both in the continuum and on the lattice. They agree in all cases where comparisons are possible. This agreement occurs with trivial measure ρ(T ) = 1. In higher dimensions, it may be necessary to utilize a non-trivial measure term in order to obtain an acceptable lattice theory. In this paper, the three-dimensional model is modified s...