PERCOLATION AND DISORDERED SYSTEMS Geoffrey GRIMMETT
PERCOLATION AND DISORDERED SYSTEMS Geoffrey GRIMMETT
PERCOLATION AND DISORDERED SYSTEMS Geoffrey GRIMMETT
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x<br />
Percolation and Disordered Systems 279<br />
y<br />
x + (6n, 0)<br />
Fig. 13.4. Six copies of a rectangle having width n and height 2n may be put<br />
together to make a rectangle with size 6n by 2n. If each is crossed by an open path<br />
joining the images of x and y, then the larger rectangle is crossed between its shorter<br />
sides.<br />
Fig. 13.5. If each of four rectangles having dimensions 6n by 2n is crossed by an<br />
open path between its shorter sides, then the annulus contains an open circuit having<br />
the origin in its interior.<br />
We now use four copies of the rectangle [0, 6n]×[0, 2n] to construct an annulus<br />
around the origin (see Figure 13.5). If each of these copies contains an open<br />
crossing, then the annulus contains a circuit. Using the FKG inequality again,<br />
we deduce that<br />
(13.48) φ 0 �<br />
p,q(A4n) ≥<br />
λn<br />
(2n + 1) 2<br />
� 24<br />
.<br />
Finally, if 0 ↔ ∂B(n), then one of the four rectangles [0, n] × [−n, n],<br />
[−n, n] × [0, n], [−n, 0] × [−n, n], [−n, n] × [−n, 0] is traversed by an open<br />
path betwen its two longer sides. This implies that<br />
(13.49) φ 0 � �<br />
p,q 0 ↔ ∂B(n) ≤ 4λn.<br />
Combining (13.46)–(13.49), we obtain that<br />
φ 0 � � �<br />
p,q 0 ↔ ∂B(n) ≤ 4 (2n + 1) 2 φ 0 p,q (A4n)<br />
�1/24 �<br />
≤ 4 (2n + 1) 2<br />
∞�<br />
�<br />
mam q<br />
q (1 + √ q) 4<br />
� �<br />
m/4<br />
1/24<br />
.<br />
m=4n<br />
As before, m −1 log am → µ as m → ∞, whence part (c) follows. �