# Dense forests and Danzer sets Academic Article

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### abstract

• A set \$Y\subseteq\mathbb{R}^d\$ that intersects every convex set of volume \$1\$ is called a Danzer set. It is not known whether there are Danzer sets in \$\mathbb{R}^d\$ with growth rate \$O(T^d)\$. We prove that natural candidates, such as discrete sets that arise from substitutions and from cut-and-project constructions, are not Danzer sets. For cut and project sets our proof relies on Ratner's theorems on homogeneous flows and on the structure of lattices in algebraic groups. We consider a weakening of the Danzer problem, the existence of a uniformly discrete dense forests, and we use homogeneous dynamics to construct such sets. We also prove an equivalence between the above problem and a well-known combinatorial problem, and deduce the existence of Danzer sets with growth rate \$O(T^d\log T)\$, improving the previous bound of \$O(T^d\log^{d-1} T)\$.

### publication date

• January 1, 2016