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PERCOLATION AND DISORDERED SYSTEMS Geoffrey GRIMMETT

PERCOLATION AND DISORDERED SYSTEMS Geoffrey GRIMMETT

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Hence,<br />

Percolation and Disordered Systems 219<br />

�<br />

Pp 0 ↔ x, u ↔ y off CB(x) � ≥ Ep<br />

We have proved that<br />

�<br />

Pp 0 ↔ x, u ↔ y off CB(x) � ≥<br />

= Ep<br />

�<br />

�<br />

Ep 1{0↔x}τ CB(x)<br />

p<br />

�<br />

1{0↔x}τ CB(x)<br />

p<br />

� �<br />

τp(0, x)τp(u, y) − Ep 1{0↔x}τp(u, y) � − Ep<br />

Applying (8.20a), we have that<br />

τp(u, y) − τ CB(x)<br />

p (u, y) ≤ �<br />

w∈CB(x)<br />

(u, y) � .<br />

(u, y) � �CB(x) ��<br />

�<br />

1{0↔x}τ CB(x)<br />

p (u, y) ��<br />

.<br />

τp(u, w)τp(y, w),<br />

whence<br />

�<br />

(8.20c) Pp 0 ↔ x, u ↔ y off CB(x) � ≥<br />

τp(0, x)τp(u, y) − � � �<br />

Pp 0 ↔ x, w ↔ x off B τp(u, w)τp(y, w).<br />

w∈Z d \B<br />

Finally, using the BK inequality,<br />

� � �<br />

Pp 0 ↔ x, w ↔ x off B ≤<br />

v∈Z d \B<br />

τp(0, v)τp(w, v)τp(x, v).<br />

We insert this into (8.20c), and deduce via (8.20b) that<br />

(8.20)<br />

(8.21)<br />

By (8.12),<br />

dχ<br />

dp<br />

≥ 2dα(p)χ2<br />

�<br />

1 − sup<br />

�<br />

|u|=1<br />

v,w/∈B<br />

�<br />

τp(0, v)τp(v, w)τp(w, u) .<br />

�<br />

τp(0, v)τp(v, w)τp(w, u) ≤ T(p) for all u.<br />

v,w<br />

Assuming that T(pc) < ∞, we may choose B = B(R) sufficiently large that<br />

(8.22)<br />

dχ<br />

dp ≥ 2dα(p)χ2 (1 − 1<br />

2 ) for p ≤ pc.<br />

Integrate this, as for (8.15), to obtain that<br />

χ(p) ≤<br />

1<br />

α ′ (pc − p)<br />

for p ≤ pc

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