Scaling for the Percolation Backbone

Abstract

We study the backbone connecting two given sites of a two-dimensional lattice separated by an arbitrary distance $r$ in a system of size $L$. We find a scaling form for the average backbone mass: $<M_B>\sim L^{d_B}G(r/L)$, where $G$ can be well approximated by a power law for $0\le x\le 1$: $G(x)\sim x^ψ$ with $ψ=0.37\pm 0.02$. This result implies that $<M_B> \sim L^{d_B-ψ}r^ψ$ for the entire range $0<r<L$. We also propose a scaling form for the probability distribution $P(M_B)$ of backbone mass for a given $r$. For $r\approx L, P(M_B)$ is peaked around $L^{d_B}$, whereas for $r\ll L, P(M_B)$ decreases as a power law, $M_B^{-τ_B}$, with $τ_B\simeq 1.20\pm 0.03$. The exponents $ψ$ and $τ_B$ satisfy the relation $ψ=d_B(τ_B-1)$, and $ψ$ is the codimension of the backbone, $ψ=d-d_B$.