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Related papers: Projections, Furstenberg sets, and the $ABC$ sum-p…

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We fully resolve the Furstenberg set conjecture in $\mathbb{R}^2$, that a $(s, t)$-Furstenberg set has Hausdorff dimension $\ge \min(s+t, \frac{3s+t}{2}, s+1)$. As a result, we obtain an analogue of Elekes' bound for the discretized…

Classical Analysis and ODEs · Mathematics 2025-01-22 Kevin Ren , Hong Wang

This paper contains new results on two classical topics in fractal geometry: projections, and intersections with affine planes. To keep the notation of the abstract simple, we restrict the discussion to the planar cases of our theorems. Our…

Classical Analysis and ODEs · Mathematics 2016-07-27 Pertti Mattila , Tuomas Orponen

Let $0 \leq s \leq 1$ and $0 \leq t \leq 2$. An $(s,t)$-Furstenberg set is a set $K \subset \mathbb{R}^{2}$ with the following property: there exists a line set $\mathcal{L}$ of Hausdorff dimension $\dim_{\mathrm{H}} \mathcal{L} \geq t$…

Classical Analysis and ODEs · Mathematics 2025-03-31 Tuomas Orponen , Pablo Shmerkin

In this paper we come up with a dual version of the Furstenberg problem and obtain partial results via $L^p$ estimates of orthogonal projections. Examples are also discussed. Moreover, compared with general sets, we find that special…

Classical Analysis and ODEs · Mathematics 2024-12-10 Longhui Li , Bochen Liu

Let $0 \leq s \leq 1$. A set $K \subset \mathbb{R}^{2}$ is a Furstenberg $s$-set, if for every unit vector $e \in S^{1}$, some line $L_{e}$ parallel to $e$ satisfies $$\dim_{\mathrm{H}} [K \cap L_{e}] \geq s.$$ The Furstenberg set problem,…

Classical Analysis and ODEs · Mathematics 2017-09-25 Tuomas Orponen

We establish several optimal estimates for exceptional parameters in the projection of fractal measures: (1) For a parametric family of self-similar measures satisfying a transversality condition, the set of parameters leading to a…

Dynamical Systems · Mathematics 2025-10-09 Meng Wu

In this paper we study multi-parameter projection theorems for fractal sets. With the help of these estimates, we recover results about the size of $A \cdot A+...+A \cdot A$, where $A$ is a subset of the real line of a given Hausdorff…

Classical Analysis and ODEs · Mathematics 2011-06-29 B. Erdoğan , D. Hart , A. Iosevich

It is shown that if $A$ is a Borel subset of the first Heisenberg group, with Hausdorff dimension satisfying $2< \dim A < 3$, then the packing dimensions of vertical projections of $A$ are almost surely not less than $\dim A$, where both…

Classical Analysis and ODEs · Mathematics 2026-03-10 Terence L. J. Harris

We show that the Hausdorff dimension of $(s,t)$-Furstenberg sets is at least $s+t/2+\epsilon$, where $\epsilon>0$ depends only on $s$ and $t$. This improves the previously best known bound for $2s<t\le 1+\epsilon(s,t)$, in particular…

Classical Analysis and ODEs · Mathematics 2024-12-18 Pablo Shmerkin , Hong Wang

We prove a version of Bourgain's projection theorem for parametrized families of $C^2$ maps, that refines the original statement even in the linear case. As one application, we show that if $A$ is a Borel set of Hausdorff dimension close to…

Classical Analysis and ODEs · Mathematics 2024-08-19 Pablo Shmerkin

We provide exposition into the field of projection theory, which lies at the intersection of incidence geometry and geometric measure theory. We first give the necessary preliminaries in Chapter 2, focusing on incidences between points and…

Classical Analysis and ODEs · Mathematics 2025-09-30 Paige Bright

In this paper we construct a new family of sets based on Diophantine approximation in the Euclidean space, and consider their applications in several problems in harmonic analysis. Our first application is on the Hausdorff dimension of our…

Classical Analysis and ODEs · Mathematics 2026-01-28 Longhui Li , Bochen Liu

The purpose of this paper is to complete the proof of the following result. Let $0 < \beta \leq \alpha < 1$ and $\kappa > 0$. Then, there exists $\eta > 0$ such that whenever $A,B \subset \mathbb{R}$ are Borel sets with $\dim_{\mathrm{H}} A…

Classical Analysis and ODEs · Mathematics 2022-01-04 Tuomas Orponen

We prove new bounds on the dimensions of distance sets and pinned distance sets of planar sets. Among other results, we show that if $A\subset\mathbb{R}^2$ is a Borel set of Hausdorff dimension $s>1$, then its distance set has Hausdorff…

Classical Analysis and ODEs · Mathematics 2019-12-17 Tamás Keleti , Pablo Shmerkin

Considerable attention has been given to the study of the arithmetic sum of two planar sets. We focus on understanding the measure and dimension of $A+\Gamma:=\left\{a+v:a\in A, v\in \Gamma \right\}$ when $A\subset \mathbb{R}^2$ and…

Classical Analysis and ODEs · Mathematics 2022-08-15 Károly Simon , Krystal Taylor

By juxtaposing ideas from fractal geometry and dynamical systems, Furstenberg proposed a series of conjectures in the late 1960's that explore the relationship between digit expansions with respect to multiplicatively independent bases. In…

Number Theory · Mathematics 2025-01-09 Daniel Glasscock , Joel Moreira , Florian K. Richter

We use recent advances on the discretized sum-product problem to obtain new bounds on the Hausdorff dimension of planar $(\alpha,2\alpha)$-Fursterberg sets. This provides a quantitative improvement to the $2\alpha+\epsilon$ bound of…

Classical Analysis and ODEs · Mathematics 2022-11-09 Daniel Di Benedetto , Joshua Zahl

Utilising recent advances in incidence geometry for balls and tubes, and advances in sum-product theory in the discrete setting, we show that for $0 < s \leq 1/2$ and for any $A \subset \mathbb{R}$ with Hausdorff dimension $s$, either the…

Classical Analysis and ODEs · Mathematics 2026-04-27 Adam Cushman , William O'Regan

We provide several new answers on the question: how do radial projections distort the dimension of planar sets? Let $X,Y \subset \mathbb{R}^{2}$ be non-empty Borel sets. If $X$ is not contained on any line, we prove that \[ \sup_{x \in X}…

Classical Analysis and ODEs · Mathematics 2024-08-19 Tuomas Orponen , Pablo Shmerkin , Hong Wang

This paper studies the Hausdorff dimension of the intersection of isotropic projections of subsets of $\mathbb{R}^{2n}$, as well as dimension of intersections of sets with isotropic planes. It is shown that if $A$ and $B$ are Borel subsets…

Metric Geometry · Mathematics 2020-01-17 Fernando Roman-Garcia
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