Random walks on intersecting geometries.

We present an analytical approach to study simple symmetric random walks on a crossing geometry consisting of a plane square lattice crossed by n_{l} number of lines that all meet each other at a single point (the origin) on the plane. The probability density to find the walker at a given distance from the origin either in a line or in the plane geometry is exactly calculated as a function of time t. We find that the large-time asymptotic behavior of the walker for any arbitrary number n_{l} of lines is eventually governed by the diffusion of the walker on the plane after a crossover time approximately given by t_{c}∝n_{l}^{2}. We show that this competition can be changed in favor of the line geometry by switching on an arbitrarily small perturbation of a drift term in which even a weak biased walk is able to drain the whole probability density into the line at long-time limit. We also present the results of our extensive simulations of the model which perfectly support our analytical predictions. Our method can, however, be simply extended to other crossing geometries with a single common point.