The small-ball to Fourier-decay conjecture for polynomial images

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Let X∼μX\sim\mu, where μ\mu is a log-concave measure on Rn\mathbb{R}^n, and let f:Rn→Rf:\mathbb{R}^n\to\mathbb{R} be a polynomial of degree dd. For a Borel measure ν\nu on R\mathbb{R}, write F(ν)(t)=∫eitx dν(x)\mathcal{F}(\nu)(t)=\int e^{\mathrm{i}tx}\,d\nu(x), and let f∗μf_*\mu denote the pushforward of μ\mu under ff. The small-ball to Fourier-decay conjecture. Suppose that for some C>0C>0 and some α∈(1/d,1)\alpha\in(1/d,1),

sup⁡a∈RP(∣f(X)−a∣≤ε)≤Cεα,for every ε>0.\sup_{a\in\mathbb{R}}\mathbb{P}\left(|f(X)-a|\leq\varepsilon\right)\leq C\varepsilon^\alpha,\qquad\text{for every }\varepsilon>0.

Then there is a constant C′C', depending only on CC and dd, such that

∣F(f∗μ)(t)∣≤C′∣t∣α,for every t≠0.|\mathcal{F}(f_*\mu)(t)|\leq\frac{C'}{|t|^\alpha},\qquad\text{for every }t\neq0.

This would improve the general exponent 1/d1/d in the Fourier-decay bound for polynomial images when stronger small-ball estimates are available. The surrounding discussion presents it as an open question, and no resolution is supplied.

References

Primary source

Itay Glazer and Dan Mikulincer, “Anti-concentration of polynomials: L^p balls and symmetric measures”, arXiv:2603.22664 (2026).

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