## The Annals of Probability

### Optimization of Shape In Continuum Percolation

Johan Jonasson

#### Abstract

We consider a version of the Boolean (or Poisson blob) continuum percolation model where, at each point of a Poisson point process in the Euclidean plane with intensity $\lambda$, a copy of a given compact convex set $A$ with fixed rotation is placed. To each $A$ we associate a critical value $\lambda_c (A)$ which is the infimum of intensities $\lambda$ for which the occupied component contains an unbounded connected component. It is shown that $\min\{\lambda_c(A):A \text{convex of area} a\} is attained if$A$is any triangle of area$a$and$\max\{\lambda_c(A):A \text{convex of area} a\} is attained for some centrally symmetric convex set $A$ of area $a$.

It turns out that the key result, which is also of independent interest, is a strong version of the difference­body inequality for convex sets in the plane. In the plane, the difference­body inequality states that for any compact convex set $A, 4\mu (A) \le \mu (A \oplus \check{A}) \le 6\mu (A)$ with equality to the left iff $A$ is centrally symmetric and with equality to the right iff $A$ is a triangle. Here $\mu$ denotes area and $A \oplus \check{A}$ is the difference­body of $A$. We strengthen this to the following result: For any compact convex set $A$ there exist a centrally symmetric convex set $C$ and a triangle $T$ such that $\mu(C) = \mu(T) = \mu(A)$ and $C \oplus \check{C} \subseteq A \oplus \check{A} \subseteq T \oplus \check{T}$ with equality to the left iff $A$ is centrally symmetric and to the right iff $A$ is a triangle.

#### Article information

Source
Ann. Probab., Volume 29, Number 2 (2001), 624-635.

Dates
First available in Project Euclid: 21 December 2001

Permanent link to this document
https://projecteuclid.org/euclid.aop/1008956687

Digital Object Identifier
doi:10.1214/aop/1008956687

Mathematical Reviews number (MathSciNet)
MR1849172

Zentralblatt MATH identifier
1013.60082

#### Citation

Jonasson, Johan. Optimization of Shape In Continuum Percolation. Ann. Probab. 29 (2001), no. 2, 624--635. doi:10.1214/aop/1008956687. https://projecteuclid.org/euclid.aop/1008956687

#### References

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• Rogers, C. A. and Shepard, G. C. (1957). The difference-body of a convex body. Arch. Math. 8 220-233.
• Schneider, R. (1993). Convex Bodies: The Brunn-Minkowski Theory. Cambridge Univ. Press.