Random induced subcomplexes of type A buildings are asymptotically spherical

Let Δk,n\Delta_{k,n} be the finite spherical building of type AkA_k, let P(Δk,n)\mathcal{P}(\Delta_{k,n}) denote its induced subcomplexes, and let S(Δk,n)\mathcal{S}(\Delta_{k,n}) denote the set of induced subcomplexes that are spherical and have the same dimension as Δk,n\Delta_{k,n}. The spherical-subcomplex conjecture. For every natural number kk,

limnS(Δk,n)P(Δk,n)=1.\lim_{n \rightarrow \infty} \frac{\left\lvert \mathcal{S}(\Delta_{k,n}) \right\rvert}{\left\lvert \mathcal{P}(\Delta_{k,n}) \right\rvert}=1.

This asserts that almost every induced subcomplex is a top-dimensional spherical complex, strengthening the preceding result that almost every induced subcomplex has nontrivial top-dimensional reduced homology. The conjecture is presented as an expected statement and no resolution is given.

Sources & referencesView supporting material

Primary source

Eduard Schesler and Matthew C. B. Zaremsky, “Random subcomplexes of finite buildings, and fibering of commutator subgroups of right-angled Coxeter groups”, arXiv:2107.10958 (2022).

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