Sharpness of the phase transition in percolation models
Abstract
The equality of two critical points — the percolation threshold p _{ H } and the point p _{ T } where the cluster size distribution ceases to decay exponentially — is proven for all translation invariant independent percolation models on homogeneous ddimensional lattices ( d≧1). The analysis is based on a pair of new nonlinear partial differential inequalities for an order parameter M(β, h), which for h=0 reduces to the percolation density P _{∞} — at the bond density p=1 e ^{ β } in the single parameter case. These are: (1) M≦ h∂ M/∂ h+ M ^{2}+β M∂ M/∂β, and (2) ∂ M/∂β≦ J M∂ M/∂ h. Inequality (1) is intriguing in that its derivation provides yet another hint of a “ϕ^{3} structure” in percolation models. Moreover, through the elimination of one of its derivatives, (1) yields a pair of ordinary differential inequalities which provide information on the critical exponentshat β and δ. One of these resembles an Ising model inequality of Fröhlich and Sokal and yields the mean field bound δ≧2, and the other implies the result of Chayes and Chayes thathat β ≤q 1. An inequality identical to (2) is known for Ising models, where it provides the basis for Newman's universal relationhat β (δ  1) ≥q 1 and for certain extrapolation principles, which are now made applicable also to independent percolation. These results apply to both finite and long range models, with or without orientation, and extend to periodic and weakly inhomogeneous systems.
 Publication:

Communications in Mathematical Physics
 Pub Date:
 September 1987
 DOI:
 10.1007/BF01212322
 Bibcode:
 1987CMaPh.108..489A