Baker–Schmidt-type algebraic approximation conjecture on the Cantor set

Let KK be the middle-third Cantor set, let κ=dimHK\kappa=\operatorname{\dim_{H}}K, and let wn(ξ)w_n^{\ast}(\xi) be the exponent governing approximation of ξ\xi by algebraic numbers of degree at most nn. Define Un(w)={ξR:wn(ξ)w}\mathcal{U}_n(w^{\ast})=\{\xi\in\mathbb{R}:w_n^{\ast}(\xi)\geq w^{\ast}\}. Baker–Schmidt-type algebraic approximation conjecture. For any integer n1n\geq 1 and any real number wnw^{\ast}\geq n, the set of points in the middle-third Cantor set which are approximable at order at least w+1w^{\ast}+1 by algebraic numbers of degree at most nn satisfies

dimH(Un(w)K)=max{n+1w+1+κ1,κw+1}.\operatorname{\dim_{H}}(\mathcal{U}_n(w^{\ast})\cap K)=\max\left\{\frac{n+1}{w^{\ast}+1}+\kappa-1,\frac{\kappa}{w^{\ast}+1}\right\}.

This is proposed as a natural extension of the paper’s main Cantor-set dimension conjecture. The source also records an open problem asking for this Hausdorff dimension, and mentions partial results toward the conjectural formula, but does not establish the formula in full.

Sources & referencesView supporting material

Primary source

Yann Bugeaud and Arnaud Durand, “Metric Diophantine approximation on the middle-third Cantor set”, arXiv:1305.6501 (2013).

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