The perturbed-metric conjecture for Gaussian noise stability deficit

Let 0<ρ<10<\rho<1 and let ARnA\subset\mathbb R^n be measurable with 0<γn(A)<10<\gamma^n(A)<1. Write v=v(H(A))/v(H(A))v=v(H(A))/|v(H(A))|, and let μ\mu and ν\nu be the push-forwards under xv,xx\mapsto\langle v,x\rangle of Gaussian measure restricted to AA and H(A)H(A), respectively. If ff and gg are their densities with respect to γ1\gamma^1, define

ε~ρ(A)=RΦ(ρxα1ρ2)(g(x)f(x))dγ1(x).\tilde \varepsilon_\rho(A)=\left|\int_{\mathbb R}\Phi\left(\frac{\rho x-\alpha}{\sqrt{1-\rho^2}}\right)(g(x)-f(x))\,d\gamma^1(x)\right|.

The perturbed-metric conjecture. For every 0<s<10<s<1, there exist constants Cs,cs>0C_s,c_s>0 such that, whenever ε(A)<e1/ρ\varepsilon(A)<e^{-1/\rho},

Cγ(A)ε~ρ(A)Sρ(H(A))Sρ(A)cγ(A)ε~ρ(A)(1ρ).C_{\gamma(A)}\tilde \varepsilon_\rho(A)\geq \mathcal{S}_\rho(H(A))-\mathcal{S}_\rho(A)\geq c_{\gamma(A)}\tilde \varepsilon_\rho(A)(1-\rho).

In particular, the Gaussian noise stability deficit should be equivalent, up to constants depending only on ρ\rho and γ(A)\gamma(A), to an expression depending only on the marginal of AA in the direction vv. The conjecture is motivated by the possibility that a slightly perturbed metric removes the logarithmic loss caused by tail phenomena; its resolution is not supplied in the source.

Sources & referencesView supporting material

Primary source

Ronen Eldan, “A two-sided estimate for the Gaussian noise stability deficit”, arXiv:1307.2781 (2014).

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