Density theorems for anisotropic point configurations

• Published in: Canadian journal of mathematics Vol. 74; no. 5; pp. 1244 - 1276
• Main Author: Kovač, Vjekoslav
• Format: Journal Article
• Language: English
• Published: Canada Canadian Mathematical Society 01.10.2022; Cambridge University Press
• Subjects: Apexes; Combinatorial analysis; Configurations; Density; Euclidean geometry; Euclidean space; Fixed points (mathematics); Graphs; Operators (mathematics); Theorems; Trees (mathematics); 28A75; 05D10; Euclidean Ramsey theory; 42B20; point configuration; singular integral; heat flow; distance graph
• ISSN: 0008-414X; 1496-4279
• DOI: 10.4153/S0008414X21000225

Several results in the existing literature establish Euclidean density theorems of the following strong type. These results claim that every set of positive upper Banach density in the Euclidean space of an appropriate dimension contains isometric copies of all sufficiently large elements of a prescribed family of finite point configurations. So far, all results of this type discussed linear isotropic dilates of a fixed point configuration. In this paper, we initiate the study of analogous density theorems for families of point configurations generated by anisotropic dilations, i.e., families with power-type dependence on a single parameter interpreted as their size. More specifically, we prove nonisotropic power-type generalizations of a result by Bourgain on vertices of a simplex, a result by Lyall and Magyar on vertices of a rectangular box, and a result on distance trees, which is a particular case of the treatise of distance graphs by Lyall and Magyar. Another source of motivation for this paper is providing additional evidence for the versatility of the approach stemming from the work of Cook, Magyar, and Pramanik and its modification used recently by Durcik and the present author. Finally, yet another purpose of this paper is to single out anisotropic multilinear singular integral operators associated with the above combinatorial problems, as they are interesting on their own.