Non-concentrated directions conjecture for projections of planar sets

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Assume that K⊂B(0,1)⊂R2K \subset B(0,1) \subset \mathbb{R}^{2} is a set with H∞1(K)∼1\mathcal{H}^{1}_{\infty}(K) \sim 1. Let E⊂S1E \subset S^{1} be a δ\delta-separated set of directions with cardinality ∣E∣∼δ−s|E| \sim \delta^{-s}, satisfying the non-concentration hypothesis

∣E∩B(x,t)∣≲tκ∣E∣,x∈S1, t≥δ,|E \cap B(x,t)| \lesssim t^{\kappa}|E|, \qquad x \in S^{1}, \: t \geq \delta,

for some κ>0\kappa > 0. Non-concentrated directions conjecture. There exists ϵ>0\epsilon > 0, depending only on κ,s\kappa,s, such that

N(πe(K),δ)≥δ−s−ϵN(\pi_{e}(K),\delta) \geq \delta^{-s - \epsilon}

for some e∈Ee \in E. The conjecture asks whether quantitative non-concentration of the directions forces at least one projection to have more than the baseline number of δ\delta-intervals; the supplied material does not indicate whether this remains open or has been resolved.

References

Primary source

Tuomas Orponen, “Projections of planar sets in well-separated directions”, arXiv:1504.07189 (2016).

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