Fässler–Orponen projection conjecture for non-degenerate curves on the sphere

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Let γ:[0,1]→S2\gamma:[0,1]\to\mathbb S^2 be a C2C^2 curve satisfying

det⁡(γ,γ′,γ”)(θ)≠0,∀ θ∈[0,1].\det(\gamma,\gamma',\gamma”)(\theta)\ne 0,\quad \forall\,\theta\in[0,1].

For each θ\theta, let pγ(θ)p_{\gamma(\theta)} denote projection onto the line in direction γ(θ)\gamma(\theta), and let πγ(θ)\pi_{\gamma(\theta)} denote projection onto the plane orthogonal to γ(θ)\gamma(\theta). Fässler–Orponen's conjecture. For every Borel set A⊆R3A\subseteq\mathbb R^3,

dim⁡pγ(θ)(A)=min⁡{1,dim⁡A},dim⁡πγ(θ)(A)=min⁡{2,dim⁡A}\dim p_{\gamma(\theta)}(A)=\min\{1,\dim A\},\qquad \dim \pi_{\gamma(\theta)}(A)=\min\{2,\dim A\}

both hold for L1\mathcal L^1-almost every θ∈[0,1]\theta\in[0,1]. This is a restricted projection conjecture for directions lying on a non-degenerate curve on the sphere; the supplied text attributes it to Fässler and Orponen but gives no resolution, so its status is left open.

References

Primary source

Tainara Borges, Siddharth Mulherkar and Tongou Yang, “Study guide for "On restricted projections to planes in R^3"”, arXiv:2403.17989 (2024).

Additional references

2 papers in this index state this conjecture (2021–2024). The statement above is taken from the most recent of them; the others are arXiv:2107.14701.

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