INFINITE PATHS ON A RANDOM ENVIRONMENT OF Z^2 WITH BOUNDED AND RECURRENT SUMS

This paper considers a random structure on the lattice Z 2 of the following kind. To each edge e a random variable Xe is assigned, together with a random sign Y_e ∈ {−1, +1}. For an infinite self-avoiding path on Z 2 starting at the origin consider the sequence of partial sums along the path. These are computed by summing the Xe’s for the edges e crossed by the path, with a sign depending on the direction of the crossing. If the edge is crossed rightward or upward the sign is given by Ye, otherwise by −Ye. We assume that the sequence of Xe’s is i.i.d., drawn from an arbitrary common law and that the sequence of signs Ye is independent, with independent components drawn from a law which is allowed to change from horizontal to vertical edges. First we show that, with positive probability, there exists an infinite self-avoiding path starting from the origin with bounded partial sums. Moreover the process of partial sums either returns to zero or at least it returns to any neighborhood of zero infinitely often. These results are somewhat surprising at the light of the fact that, under rather mild conditions, there exists with probability 1 two sites with all the paths joining them having the partial sums exceeding in absolute value any prescribed constant.