Unbounded rank super-expanders conjecture

A super-expander is a sequence of finite Cayley graphs whose expansion persists with respect to every uniformly convex Banach space, with suitable finite generating sets. Let SL(n,Fp)\mathrm{SL}(n,\mathbb{F}_p) denote the special linear group over the finite field with pp elements, and let (Buc)(\mathcal{B}_{\mathrm{uc}}) denote the class of uniformly convex Banach spaces. Unbounded rank super-expanders conjecture. (1) For every prime pp, the sequence (SL(n,Fp))n4(\mathrm{SL}(n,\mathbb{F}_p))_{n\geq 4} can form super-expanders. (2) For every sequence of primes (pn)n(p_n)_n, (SL(n,Fpn))n4(\mathrm{SL}(n,\mathbb{F}_{p_n}))_{n\geq 4} can form super-expanders. (3) The family of all simple groups of Lie type and rank at least 33 has a mother group with property (FBuc)\mathrm{(F}_{\mathcal{B}_{\mathrm{uc}}}\mathrm{)}. The conjecture concerns the existence of super-expanders in unbounded rank and a fixed-point formulation for families of finite simple groups of Lie type; the paper reduces the special-linear-group case to relative property (T)(\mathrm{T}) with respect to uniformly convex Banach spaces, but the conjectured assertions remain unresolved.

Sources & referencesView supporting material

Primary source

Masato Mimura, “Strong algebraization of fixed point properties”, arXiv:1505.06728 (2016).

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