Exponential concentration implies a finite Poincaré constant

Let g(t)=exp(tet)g(t)=\exp(t-e^t), and let γ(x,ξ)=exp(axbξ)\gamma(x,\xi)=\exp(-a|x|-b|\xi|) with a,b>0a,b>0. Suppose that fL2(R)f\in L^2(\mathbb{R}) has exponential time-frequency concentration, meaning

δ>0:Vgf(z)eδzL(R2).\exists\,\delta>0:\quad |\mathcal{V}_g f(z)|\cdot e^{\delta|z|}\in L^\infty(\mathbb{R}^2).

Let w=(Vgf2γ)2w=(|\mathcal{V}_g f|^2\ast\gamma)^2. Exponential-concentration conjecture. The weighted measure defined by ww has finite Poincaré constant:

CP(w)<.C_P(w)<\infty.

Exponential concentration is known to follow from a Poincaré inequality, but the converse is not generally true for weights with disconnected support. In this setting, however, the weights are strictly positive because they arise from convolution with γ\gamma, so the question is whether exponential time-frequency concentration is sufficient for a finite Poincaré constant.

Sources & referencesView supporting material

Primary source

Martin Rathmair, “Stable STFT phase retrieval and Poincaré inequalities”, arXiv:2407.00398 (2024).

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