Eskenazis–Ivanisvili's dimension-free heat-semigroup lower bound

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Let (X,∥⋅∥X)(X,\|\cdot\|_X) be a KK-convex Banach space. For n∈Nn\in\mathbb{N}, let Deg⁡≤d\operatorname{Deg}_{\le d} denote the space of functions f:{−1,1}n→Xf:\{-1,1\}^n\to X whose Hamming cube Fourier–Walsh expansion has no terms of degree greater than dd. Let Δ\Delta be the Hamming cube Laplacian and let e−tΔe^{-t\Delta} be its heat semigroup, defined by e−tΔwS=e−t∣S∣wSe^{-t\Delta}w_S=e^{-t|S|}w_S. Eskenazis–Ivanisvili's conjecture. For every p∈(1,∞)p\in(1,\infty), there exist constants c(p,X)c(p,X) and C(p,X)C(p,X) such that, for every d∈[n]d\in[n], every f∈Deg⁡≤df\in\operatorname{Deg}_{\le d} and every t≥0t\ge0,

∥e−tΔf∥Lp({−1,1}n;X)≥c(p,X) exp⁡(−C(p,X) td) ∥f∥Lp({−1,1}n;X).\|e^{-t\Delta}f\|_{L^p(\{-1,1\}^n;X)}\ge c(p,X)\,\exp(-C(p,X)\,td)\,\|f\|_{L^p(\{-1,1\}^n;X)}.

This is a dimension-free lower bound quantifying how much the heat semigroup can damp a low-degree function. The source says that it gives partial answers in the special case where ff takes values in {−1,0,1}\{-1,0,1\} and X=CX=\mathbb{C}, so the general statement remains open in the paper's presentation.

References

Primary source

Komla Domelevo, Polona Durcik, Valentia Fragkiadaki, Ohad Klein, Diogo Oliveira e Silva, Lenka Slavíková and Błażej Wróbel, “Dimension-free estimates for low degree functions on the Hamming cube”, arXiv:2401.07699 (2024).

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