Gap conjectures for heat kernel, Følner function, isoperimetric profile and spectral density

Let GG be a finitely generated amenable group, with the heat-kernel function P(n)P(n), Følner function F(n)\mathcal F(n), isoperimetric profile Λ(n)\Lambda(n), and spectral density N(λ)\mathcal N(\lambda) as defined in the source. Let β,γ,ρ,δ\beta,\gamma,\rho,\delta be positive parameters. Gap conjectures with parameters. The following alternatives should hold: P(n)P(n) has power-rate decay nd/2n^{-d/2} or satisfies P(n)enβP(n)\preceq e^{-n^\beta}; F(n)\mathcal F(n) has polynomial growth ndn^d or grows at least as fast as enγe^{n^\gamma}; Λ(n)\Lambda(n) has power-rate decay nd/2n^{-d/2} or satisfies Λ(n)(logn)ρ\Lambda(n)\succeq(\log n)^{-\rho}; and N(λ)\mathcal N(\lambda) has power decay of type λd/2\lambda^{d/2} near zero for some dNd\in\mathbb N, or satisfies N(λ)eλδ\mathcal N(\lambda)\succeq e^{-\lambda^{-\delta}} near zero. These conjectures concern gaps between polynomial behavior and slower-than-polynomial behavior; the polynomial cases are known for groups of polynomial growth, but the source does not resolve the proposed alternatives.

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Primary source

Rostislav Grigorchuk, “On the Gap Conjecture concerning group growth”, arXiv:1202.6044 (2012).

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