Fourier lower-bound conjecture for sofic lpl^{p} dimension

Let Γ\Gamma be a sofic group and fix 1p21\leq p\leq 2. Set M=L(Γ)M=L(\Gamma), let τ\tau be the canonical group trace, and let pp' satisfy 1/p+1/p=11/p+1/p'=1. Let F ⁣:lp(Γ)Lp(M,τ)\mathcal{F}\colon l^{p}(\Gamma)\to L^{p'}(M,\tau) be the Fourier transform. For Xlp(Γ)X\subseteq l^{p}(\Gamma), let qMq\in M be a projection satisfying

F(X)p=Lp(M,τ)q.\overline{\mathcal{F}(X)}^{\|\cdot\|_{p}}=L^{p}(M,\tau)q.

The Fourier lower-bound conjecture.

dimΣ,lp(X,Γ)τ(g).\underline{\dim}_{\Sigma,l^{p}}(X,\Gamma)\geq \tau(g).

Moreover, if Γ\Gamma is Rω\mathcal{R}^{\omega}-embeddable, with the same X,p,p,q,τX,p,p',q,\tau, then

dimΣ,Sp,conj(X,Γ)τ(q).\underline{\dim}_{\Sigma,S^{p},\operatorname{conj}}(X,\Gamma)\geq \tau(q).

The source itself warns that the conjecture may be too strong in full generality, while suggesting that special cases could still be meaningful; the first displayed bound contains τ(g)\tau(g) although the setup defines qq.

Sources & referencesView supporting material

Primary source

Ben Hayes, “An l^p-Version of von-Neumann Dimension For Banach Space Representations of Sofic Groups”, arXiv:1110.5390 (2013).

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