Non-coincidence of Quenched and Annealed Connective Constants on the   supercritical planar percolation cluster
  In this paper, we study the abundance of self-avoiding paths of a given length on a supercritical percolation cluster on $\bbZ^d$. More precisely, we count $Z_N$ the number of self-avoiding paths of length $N$ on the infinite cluster, starting from the origin (that we condition to be in the cluster). We are interested in estimating the upper growth rate of $Z_N$, $\limsup_{N\to \infty} Z_N^{1/N}$, that we call the connective constant of the dilute lattice. After proving that this connective constant is a.s.\ non-random, we focus on the two-dimensional case and show that for every percolation parameter $p\in (1/2,1)$, almost surely, $Z_N$ grows exponentially slower than its expected value. In other word we prove that $\limsup_{N\to \infty} (Z_N)^{1/N} <\lim_{N\to \infty} \bbE[Z_N]^{1/N}$ where expectation is taken with respect to the percolation process. This result can be considered as a first mathematical attempt to understand the influence of disorder for self-avoiding walk on a (quenched) dilute lattice. Our method, which combines change of measure and coarse graining arguments, does not rely on specifics of percolation on $\bbZ^2$, so that our result can be extended to a large family of two dimensional models including general self-avoiding walk in random environment. 
Hubert Lacoin
math.PR math-ph math.MP