Uniform finite-exceptional-spectrum conjecture for dense generators of compact Lie groups

Let GG be a simple compact Lie group, let k4k\geq 4, and let SS be a symmetric set of size kk generating a dense subgroup of GG. Let ΔS\Delta^S denote the associated averaging or adjacency operator. Uniform finite-exceptional-spectrum conjecture. There exists ϵ>0\epsilon>0 such that ΔS\Delta^S has only finitely many eigenvalues outside the interval

[k+ϵ,kϵ].[-k+\epsilon,k-\epsilon].

This is proposed as a stronger spectral-gap conjecture for dense generating sets; the preceding discussion relates spectral gaps to weak Diophantine properties, while uniformity over all such sets remains open.

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Primary source

Emmanuel Breuillard and Alexander Lubotzky, “Expansion in simple groups”, arXiv:1807.03879 (2018).

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