The Regge Calculus approximates a continuous manifold by a simplicial lattice, keeping the connectivities of the underlying lattice fixed and taking the edge lengths as degrees of freedom. The Discrete Regge model employed in this work limits the choice of the link lengths to a finite number. This makes the computational evaluation of the path integral much faster. A main concern in lattice field theories is the existence of a continuum limit which requires the existence of a continuous phase transition. The recently conjectured second-order transition of the four-dimensional Regge skeleton at negative gravity coupling could be such a candidate. We examine this regime with Monte Carlo simulations and critically discuss its behavior.
REGGE QUANTUM GRAVITYOne promising method to quantize the theory of gravitation employs the Euclidean path integralwhere the partition function describes a fluctuating space-time manifold. In the Regge approach the (quadratic) link lengths q l represent the dynamical degrees of freedom [1], deforming continuously a simplicial lattice with fixed incidence matrix, whereas in the somehow complementary approach of dynamical triangulation the incidence matrix is fluctuating with constant link lengths. Any of these two approaches is plagued with various problems; for the Regge approach see [2,3]. In "conventional" Regge theory the ReggeEinstein action including a cosmological term [4],is used. The first sum runs over all products of triangle area A t times corresponding deficit angle δ t weighted by the bare gravitational coupling β. * Poster presented by E. B. and supported by Hochschuljubiläumsstiftung der Stadt Wien. † W. J. acknowledges partial support by the EC IHP Network grant HPRN-CT-1999-00161: "EUROGRID".The second sum extends over the volumes V s of the 4-simplices of the lattice and allows together with the cosmological constant λ to set an overall scale in the action. The Discrete Regge model was invented in an attempt to reformulate (1) as the partition function of a spin system [5,6]. It is defined by restricting the squared link lengths to take on only two valueswhere b l = 1, 2, 3, and 4 for edges, face diagonals, body diagonals and the hyperbody diagonal of a hypercube, respectively, is chosen to allow for fluctuations around flat space. The Euclidean triangle inequalities are fulfilled automatically as long as ǫ is smaller than a maximum value ǫ max . The measure D[q] in the quantum gravity path integral is taken to unity for all possible link configurations. Numerical simulations of the Z 2 system become extremely efficient by implementing look-up tables and a heat-bath algorithm. In this work typically 200 000 − 500 000 iterations have been generated. Calculations have been performed with the parameter ǫ = 0.0875 and the cosmological constant λ = 0 because (3) already fixes the average lattice volume.