The unrestricted cylindrical width conjecture for finite transitive subsets of complex spheres

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Let 1≤k≤d1\le k\le d. Let XX be a finite transitive subset of the unit sphere in Cd\mathbb{C}^d. Unrestricted cylindrical width conjecture. There is a complex kk-dimensional subspace WW such that

sup⁡x∈X∥proj⁡Wx∥2≲1log⁡(2d/k).\sup_{\mathbf{x}\in X}\lVert\operatorname{proj}_W\mathbf{x}\rVert_2 \lesssim \frac{1}{\sqrt{\log(2d/k)}}.

The preceding theorem proves this estimate under the additional restriction k≤d/(log⁡(3d))Ck\le d/(\log(3d))^C; the authors suspect that this restriction is unnecessary, so the conjecture concerns all 1≤k≤d1\le k\le d.

References

Primary source

Ashwin Sah, Mehtaab Sawhney and Yufei Zhao, “The cylindrical width of transitive sets”, arXiv:2101.11207 (2021).

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