Universal crossing probability in anisotropic systems

Laboratoire de Physique des Matériaux, UMR CNRS 7556, Université Henri Poincaré (Nancy 1) - BP 239, 54506 Vandœuvre lès Nancy Cedex, France

Received: 2 May 2002
Accepted: 15 July 2002

Abstract

Scale-invariant universal crossing probabilities are studied for critical anisotropic systems in two dimensions. For weakly anisotropic standard percolation in a rectangular-shaped system, Cardy's exact formula is generalized using a length-rescaling procedure. For strongly anisotropic systems in 1+1 dimensions, exact results are obtained for the random walk with absorbing boundary conditions, which can be considered as a linearized mean-field approximation for directed percolation. The bond and site directed percolation problem is itself studied numerically via Monte Carlo simulations on the diagonal square lattice with either free or periodic boundary conditions. A scale-invariant critical crossing probability is still obtained, which is a universal function of the effective aspect ratio , where , z is the dynamical exponent and c is a non-universal amplitude.