The dimension bounds conjecture for restricted numerator systems

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Let Bn⊆{0,1,…,n−1}B_n\subseteq\{0,1,\dots,n-1\} for each integer nn. For an approximation function ff and an inhomogeneous shift θ\theta, define WB(f,θ)W_B(f,\theta) as the set of x∈[0,1]x\in[0,1] satisfying

∣x−m+θ(n)n∣≤f(n)n\left|x-\frac{m+\theta(n)}{n}\right|\leq\frac{f(n)}{n}

for infinitely many pairs n,mn,m with m∈Bnm\in B_n. Let W0(f,0)W_0(f,\mathbf{0}) denote the unrestricted homogeneous set. The dimension bounds conjecture. For every approximation function ff and inhomogeneous shift θ\theta,

lim inf⁡n→∞log⁡∣Bn∣log⁡ndim⁡HW0(f,0)≤dim⁡HWB(f,θ)≤lim sup⁡n→∞log⁡∣Bn∣log⁡ndim⁡HW0(f,0).\liminf_{n\to\infty}\frac{\log|B_n|}{\log n}\dim_H W_0(f,\mathbf{0})\leq\dim_H W_B(f,\theta)\leq\limsup_{n\to\infty}\frac{\log|B_n|}{\log n}\dim_H W_0(f,\mathbf{0}).

In particular, if

lim⁡n→∞log⁡∣Bn∣log⁡n=1,\lim_{n\to\infty}\frac{\log|B_n|}{\log n}=1,

then

dim⁡HW0(f,0)=dim⁡HWB(f,θ).\dim_H W_0(f,\mathbf{0})=\dim_H W_B(f,\theta).

This proposes quantitative control of the dimension loss caused by restricting the allowed numerators. The source gives no resolution.

References

Primary source

Han Yu, “A Fourier analytic approach to inhomogeneous Diophantine approximation”, arXiv:1704.04691 (2018).

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