Monotonicity conjecture for the connectivity of Čech complexes of spheres

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For n≥1n\ge 1, let SnS^n be the unit nn-sphere and let Cˇ(Sn;r)\mathrm{\check{C}}(S^n;r) denote its Čech complex at scale r∈(0,π)r\in(0,\pi). Write conn⁡(K)\operatorname{conn}(K) for the connectivity of a complex KK. Connectivity monotonicity conjecture. The function

r⟼conn⁡(Cˇ(Sn;r))r\longmapsto \operatorname{conn}(\mathrm{\check{C}}(S^n;r))

is non-decreasing on (0,π)(0,\pi). This is known for n=1n=1, and for n≥2n\ge 2 the complexes are known to be simply connected; for n≥3n\ge 3, it remains unknown whether the connectivity stays at least n−1n-1 once r≥π/2r\ge \pi/2.

References

Primary source

Henry Adams, Ekansh Jauhari and Sucharita Mallick, “Homotopy connectivity of Čech complexes of spheres”, arXiv:2502.00122 (2026).

Additional references

3 papers in this index state this conjecture (2023–2025). The statement above is taken from the most recent of them; the others are arXiv:2407.15818, arXiv:2304.01306.

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