4D SIMPLICIAL QUANTUM-GRAVITY - MATTER FIELDS AND THE CORRESPONDING EFFECTIVE ACTION

Four-dimensional simplicial quantum gravity is modified either by coup ling it to U(1) gauge fields or by introducing a measure weighted by t he orders of the triangles. Strong coupling expansion and Monte Carlo simulations are used. Although the two modifications of the standard p ure-gravity model are apparently very distinct, they produce strikingl y similar results, as far as the geometry of random manifolds is conce rned. In particular, for an appropriate choice of couplings, the branc hed polymer phase is replaced by a crinkled phase, characterized by th e susceptibility exponent gamma < 0 and the fractal dimension d(H) > 2 . The quasi-equivalence between the two models is exploited to get fur ther insight into the extended phase diagram of the theory. (C) 1998 E lsevier Science B.V. All rights reserved.