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

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Let GG be a simple compact Lie group, let k≥4k\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,k−ϵ].[-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.

References

Primary source

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

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