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Line-of-Sight Percolation

Published online by Cambridge University Press:  01 March 2009

BÉLA BOLLOBÁS
Affiliation:
Department of Mathematical Sciences, University of Memphis, Memphis TN 38152, USA and Trinity College, Cambridge CB2 1TQ, UK (e-mail: B.Bollobas@dpmms.cam.ac.uk)
SVANTE JANSON
Affiliation:
Department of Mathematics, Uppsala University, PO Box 480, SE-751 06 Uppsala, Sweden (e-mail: svante.janson@math.uu.se)
OLIVER RIORDAN
Affiliation:
Royal Society Research Fellow, Department of Pure Mathematics and Mathematical Statistics, University of Cambridge, Wilberforce Road, Cambridge CB3 0WB, UK; Mathematical Institute, University of Oxford, 24–29 St Giles, Oxford OX1 3LB, UK (e-mail: riordan@maths.ox.ac.uk)
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Abstract

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Given ω ≥ 1, let $\Z^2_{(\omega)}$ be the graph with vertex set $\Z^2$ in which two vertices are joined if they agree in one coordinate and differ by at most ω in the other. (Thus $\Z^2_{(1)}$ is precisely $\Z^2$.) Let pc(ω) be the critical probability for site percolation on $\Z^2_{(\omega)}$. Extending recent results of Frieze, Kleinberg, Ravi and Debany, we show that limω→∞ωpc(ω)=log(3/2). We also prove analogues of this result for the n-by-n grid and in higher dimensions, the latter involving interesting connections to Gilbert's continuum percolation model. To prove our results, we explore the component of the origin in a certain non-standard way, and show that this exploration is well approximated by a certain branching random walk.