Multidimensional generalisation of the Schmidt conjecture is true

You need to know: Euclidean space {\mathbb R}^n, notation {\mathbb N} for the set of positive integers. In addition, you need to know the concept of Hausdorff dimension of set A\subset {\mathbb R}^n to understand the “moreover” part of the Theorem.

Background: For x\in{\mathbb R}, let ||x|| denote the distance from x to the nearest integer. Let {\cal R}_n \subset {\mathbb R}^n be the set of r=(r_1, \dots, r_n) such that r_i\geq 0, \, i=1,\dots,n and \sum\limits_{i=1}^n r_i=1. Given \textbf{r}\in {\cal R}_n, we say that point \textbf{y}=(y_1,\dots, y_n) \in {\mathbb R}^n is \textbf{r}-badly approximable if there exists c=c(\textbf{y})>0 such that \max\limits_{1 \leq i \leq n}||qy_i||^{1/r_i} \geq c/q for all q \in {\mathbb N}, with convention that ||qy_i||^{1/0}=0. Let Bad(r) be be set of all \textbf{r}-badly approximable points in {\mathbb R}^n.

The Theorem: On 2nd April 2013, Victor Beresnevich submitted to arxiv a paper in which he proved that for any finite subset W\subset {\cal R}_n, the set \bigcap\limits_{\textbf{r}\in W} \textbf{Bad(r)} is non-empty. Moreover, this set has Hausdorff dimension n.

Short context: A real number x is said to be badly approximable if there exists a constant c(x)>0 such that ||qx|| > c(x)/q for all q \in {\mathbb N}. Sets Bad(r) are natural generalisations containing n-tuples (y_1, \dots, y_n) of simultaneously badly approximable numbers. In 1983, Schmidt conjectured that \textbf{Bad}\left(\frac{1}{3}, \frac{2}{3}\right) \cap \textbf{Bad}\left(\frac{2}{3}, \frac{1}{3}\right) \neq \emptyset. In 2011, Badziahin, Pollington, and Velani proved the n=2 case of the Theorem, which implies the Schmidt’s conjecture as a special case. The Theorem is a generalisation of this result to all dimensions.

Links: Free arxiv version of the original paper is here, journal version is here.

Go to the list of all theorems

Leave a comment