Usher's obstruction-supremum conjecture for ellipsoid embedding functions

For n1n\geq 1, define

Ln,0=n21.L_{n,0}=\sqrt{n^2-1}.

Let Ak,nA_{k,n} and A^k,n\hat A_{k,n} be Usher's obstruction classes, let μE,Ln,0\mu_{\mathbf{E},L_{n,0}} denote the obstruction associated to a class E\mathbf{E}, and let accum(Ln,0)\mathrm{accum}(L_{n,0}) be the accumulation point of the infinite staircase for cLn,0c_{L_{n,0}}. Let the center of A0,nA_{0,n} be the left endpoint of the interval under consideration.

Usher's conjecture. Between the center of A0,nA_{0,n} and accum(Ln,0)\mathrm{accum}(L_{n,0}), the function cLn,0c_{L_{n,0}} equals

sup{μE,Ln,0:E is one of the Ak,n or A^k,n}.\sup\{\mu_{\mathbf{E},L_{n,0}}:\mathbf{E}\text{ is one of the }A_{k,n}\text{ or }\hat A_{k,n}\}.

Usher proved that cLn,0c_{L_{n,0}} has an infinite staircase, while this conjecture predicts the complete embedding function up to its accumulation point using the indicated obstruction classes.

Sources & referencesView supporting material

Primary source

Caden Farley, Tara Holm, Nicki Magill, Jemma Schroder, Morgan Weiler, Zichen Wang and Elizaveta Zabelina, “Four-periodic infinite staircases for four-dimensional polydisks”, arXiv:2210.15069 (2023).

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