Cocycle Cheeger constants for Steinberg and GKKL presentations

Let SLn(Fp)SL_n(\mathbb{F}_p) be presented either by the Steinberg presentations, whose complexity is Ω(p)\Omega(p), or by the Guralnik–Kantor–Kassabov–Lubotzky (GKKL) presentations, whose complexity is logarithmic in the size of the group. Let the cocycle Cheeger constant in permutations refer to the constant associated with one of these presentations.

Cocycle-Cheeger conjecture. The cocycle Cheeger constants in permutations of the Steinberg presentations have a uniform positive lower bound, at least when nn is fixed and pp\to\infty. In contrast, the cocycle Cheeger constants in permutations of the GKKL presentations tend to zero when either nn\to\infty or pp\to\infty.

This proposes opposite asymptotic behavior for the expansive Steinberg presentations and the logarithmic-complexity GKKL presentations of finite simple groups; the source describes this case as completely open.

Sources & referencesView supporting material

Primary source

Michael Chapman and Alexander Lubotzky, “Stability of Homomorphisms, Coverings and Cocycles II: Examples, Applications and Open problems”, arXiv:2311.06706 (2024).

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