REVIEW 3 major objections 5 minor 32 references
Fractal Uncertainty and Quantitative Uniqueness for the Fourier Bessel Transform
T0 review · 3 major / 5 minor · reviewed 2026-08-27 · deepseek-v4-flash
Pith's one-line read The paper proves a fractal uncertainty principle for the Fourier–Bessel transform: if position and frequency supports are scale-regular fractals, mass decays like $h^\beta$, uniformly in the translation parameter.
desk verdict Theorem 1.3 is a genuine, mostly proved extension of the Jaye–Mitkovski uniqueness theory to the Fourier–Bessel transform; Theorem 1.4's fractal uncertainty principle is not proved as written because the centered damping functions in Remark 4.5 are asserted, not constructed, and the natural symmetrizations fail. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The central object is a damping function for a regular set $Y$: a function $\psi$ supported near the origin whose Hankel transform is bounded below by a positive constant on a neighbourhood of $Y$, decays faster than any polynomial globally, and decays against a superpolynomial weight along $Y$ itself. The construction goes through a band-limited multiplier obtained from a plurisubharmonic potential, and the paper's key move is to apply the construction to the translated set $Y-\eta$ and its reflection, producing damping functions whose constants do not depend on the translation center $\eta$. These damping functions localize $f$ through the generalized Hankel convolution, after which the large-argument asymptotic expansion of Bessel functions turns the high-frequency part of the estimate into a classical Fourier uncertainty estimate for the localized pieces. A multiscale iteration, using scale-wise porosity of $X$ to insert sharp weight functions, compounds the $h^\beta$ loss scale by scale.
What would settle it
Pick a concrete pair: $X$ a middle-thirds Cantor set scaled into $[0,1]$ and $Y$ the same Cantor construction dilated to length $h^{-1}$ and translated by $a$; compute $\|1_X f\|_{L^2_\nu}/\|f\|_{L^2_\nu}$ for $f=\mathcal H_\nu^{-1}(1_Y)$ as $h\to 0$ with $a$ growing like $a_0 h^{-1}$. The theorem predicts $O(h^\beta)$ decay with constants independent of $a$; any ratio that fails to decay, or whose constant grows with $a$ at fixed $h$, would falsify the uniform-in-$a$ claim.
Extended reading notes
Core claim
The paper's central claim is Theorem 1.4: for $\nu>-1/2$ and $0\le\delta<1$, let $X\subset[0,1]$ be $\delta$-regular with constant $C_R$ on scales $h$ to $1$, and let $Y\subset[a,a+h^{-1}]$ be $\delta$-regular with constant $C_R$ on scales $1$ to $h^{-1}$. Then there exist $a_0,\beta,C>0$, depending only on $\delta,C_R,\nu$, such that every $f\in L^2_\nu(\mathbb R_+)$ with $\operatorname{supp}\mathcal H_\nu f\subset Y$ obeys $$\|1_X f\|_{$L^{2}$_\nu}\le C h^\$\beta$ \|f\|_{$L^{2}$_\nu},\qquad a\ge a_0 $h^{{-1}}$.$$ The load-bearing feature is uniformity in $a$: the translated location of the spectral fractal does not enter the constants, even though the Hankel transform lacks the translation invariance that makes the classical Fourier argument work. The paper's second claim, Theorem 1.3, is a higher-dimensional quantitative uniqueness statement: if the Hankel transform of $f$ decays against a unique continuation weight $W$, then $\|f\|_{L^2_\nu}$ is controlled by $\|f\|_{L^2_\nu(E)}$ for any relatively dense set $E$. The one-dimensional FUP is obtained from these ingredients by splitting the spectrum into high frequencies, applying Bessel asymptotics to reduce to a Fourier-type estimate, and iterating a scale-by-scale gain.
Load-bearing premise
The argument rests on the existence of damping functions for translated copies of the frequency fractal whose constants are independent of the translation; the paper cites earlier constructions for this step rather than proving it here.
Editorial extensions
If this is right
- Theorem 1.4 supplies the first fractal uncertainty principle for the Fourier–Bessel transform in one dimension, with the translation-independent constants that any application to translated spectral fractals would require.
- Theorem 1.3 gives a quantitative unique continuation statement: an $L^2_\nu$ function whose Hankel transform decays with a quasi-analytic weight cannot be small on any relatively dense set; its global norm is controlled by the norm on that set.
- The crude $L^1_\nu\to L^\infty$ estimate diverges for $\nu>-\delta$, so the $h^\beta$ decay in Theorem 1.4 is a genuine improvement rather than a repackaging of the trivial bound.
- The multiscale proof gives an explicit exponent $\beta\approx \gamma_0/(2T\ln 2)$, depending on scale-separation parameters, so the principle is quantitative rather than purely existential.
- The restriction $a\ge a_0 h^{-1}$ means the theorem covers high-frequency spectral fractals; the low-frequency and higher-dimensional cases are explicitly not settled by the present argument.
Reading between the lines
- A natural extension the authors leave implicit is the many-window analogue: replacing the single spectral interval $[a,a+h^{-1}]$ by a union of well-separated translated regular sets, where the same damping-function construction should compound the loss with the number of components.
- The same obstruction—no translation invariance—appears for other integral transforms whose kernels are Bessel-type functions, so the damping-function strategy should transfer to Jacobi or Dunkl transforms if their Paley–Wiener theorems support it.
- If the uniform damping estimate can be pushed below the high-frequency threshold $a\ge a_0 h^{-1}$, the multiscale iteration would extend to low-frequency fractals, which the paper explicitly leaves open.
Formalized claims in Lean
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Claim #1: The paper's central claim is Theorem 1.4: for $\nu>-1/2$ and $0\le\delta<1$, let $X\subset[0,1]$ be $\delta$-regular with constant $C_R$ on scales $h$ to $1$, and let $Y\subset[a,a+h^{-1}]$ be $\delta$-regular with constant $C_R$ on scales $1$ to $h^{-1}$. Then there exist $a_0,\beta,C>0$, depending only on $\delta,C_R,\nu$, such that every $f\in L^2_\nu(\mathbb R_+)$ with $\operatorname{supp}\mat
/-- @claim 1 The paper's central claim is Theorem 1.4: for $\nu>-1/2$ and $0\le\delta<1$, let $X\subset[0,1]$ be $\delta$-regular with constant $C_R$ on scales $h$ to $1$, and let $Y\subset[a,a+h^{-1}]$ be $\delta$-regular with constant $C_R$ on scales $1$ to $h^{-1}$. Then there exist $a_0,\beta,C>0$, depending only on $\delta,C_R,\nu$, such that every $f\in L^2_\nu(\mathbb R_+)$ with $\operatorname{supp}\mat -/ def central_claim : Prop :=
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper studies quantitative uniqueness and a fractal uncertainty principle (FUP) for the one- and multidimensional Fourier–Bessel (Hankel) transform. Theorem 1.3 is a Logvinenko–Sereda-type estimate: if E is relatively dense with respect to the measure dμν and Hνf decays according to a quasi-analytic weight W, then the L2ν norm of f on the whole space is controlled by its L2ν norm on E, with an explicit necessity argument for the logarithmic-integral condition. Theorem 1.4 is the main FUP: for X⊂[0,1] that is δ-regular on scales h to 1 and Y⊂[a,a+h^{-1}] that is δ-regular on scales 1 to h^{-1}, one has ‖1_X f‖_{L2ν} ≤ C h^β ‖f‖_{L2ν} whenever supp Hνf is contained in Y, with constants independent of the translation parameter a for a ≥ a0 h^{-1}. The proof strategy is to construct translated and centered Hankel damping functions via Beurling–Malliavin theory, reduce the high-frequency estimate to the Fourier FUP through Bessel asymptotics, and then run a Bourgain–Dyatlov multiscale iteration.
Significance. If Theorem 1.4 is fully established, it is a genuine fractal uncertainty principle for the Fourier–Bessel transform and, in particular, gives h^β decay uniformly in the translation parameter a, which is the natural substitute for the lack of translation invariance of the Hankel transform. The paper is also useful in identifying the precise role of the obstacle: the damping functions must be centered at each lattice point while remaining even, since Hankel multipliers are even. The quantitative uniqueness part, Theorem 1.3, appears mostly self-contained and is interesting in its own right, extending the band-limited results of reference [30] to quasi-analytic decay. The remarks comparing the trivial L1–L∞ bound with the obtained high-frequency estimate are informative. However, the central damping construction for translated regular sets is not proved, and the proof of Proposition 4.1 contains an internal mismatch between the stated weight in the good/bad summation and the weight required by Lemma 4.6; these gaps are load-bearing for Theorem 1.4.
major comments (3)
- [Section 4.2, Lemma 4.4 and Remark 4.5] Lemma 4.4 supplies the damping functions on which the whole proof of Theorem 1.4 rests, but its proof is deferred to references [3, Lemma 3.1] and [8, Proposition 3.5], both of which are statements in the Fourier setting. More seriously, Remark 4.5 asserts, without proof, that for every η in the lattice Λ=c2N the same construction applied to Y−η and its reflection gives an even entire multiplier Fη with the uniform bounds |Fη(ξ)| ≥ c2 on B_{c2}(η) and |Fη(ξ)| ≤ 1/W(|ξ−η|) on Y. For the Hankel transform the multiplier must be even in ξ. The two natural symmetrizations fail: Fη(ξ)=G(ξ−η)+G(ξ+η) does not have the required exponential decay on the far part of Y, since G(ξ+η) is evaluated far outside the regular set and is only polynomially small there; while the product Fη(ξ)=G(ξ−η)G(ξ+η) restores decay but loses the uniform lower bound at ξ=η because G(2η) need not be bounded below independently of η. Thus the stated argument does not establish the uniform-in-η damping property, and both Proposition 4.1 and Lemma 4.7, which rely on it, are left unsupported. A different centered construction, or a proof that a symmetrized multiplier satisfies both bounds uniformly in η, is needed.
- [Section 4.2, Proposition 4.1, equations (4.22) and (4.17)] The good/bad summation in the proof of Proposition 4.1 does not close as written. Good indices are defined in (4.22) by the condition ||W(|η−·|)^{1/2} Hν fη||_{L2ν} ≤ A ||fη||_{L2ν}, but Lemma 4.6 is invoked with hypothesis (4.17), which requires ||W(|η−·|) Hν fη||_{L2ν} ≤ A ||fη||_{L2ν}. Since W(t) ≥ 1, the condition (4.22) is weaker than (4.17), so the hypotheses of Lemma 4.6 are not satisfied. The proof of Lemma 4.6 also uses a Cauchy–Schwarz splitting with W and with the integral of W^{-2}; to be compatible with (4.22) it would need the splitting with W^{1/2} and the integral of W^{-1}. This is likely repairable by changing the weights consistently, but as written the argument is internally inconsistent and Proposition 4.1 does not follow.
- [Section 4.2, Proposition 4.2] Proposition 4.2 is a key input in Lemma 4.6: the Fourier reduction requires inequality (4.15) for the two-component set Y=(Y0+a)∪(−Y0−a) with a constant independent of a. The proof is not given; the text only says that a slight modification of reference [3, Proposition 3.3] or an argument in reference [8, Proposition 3.5] gives it. Since [3, Proposition 3.3] is stated for a set on a fixed interval and the parameter a here may be as large as h^{-1}, the uniformity in a is not a formal consequence of translation invariance alone: the regularity conditions are imposed on absolute scales 1 to h^{-1}, and the two components of Y are separated by a distance that grows with a. The full statement and proof, or an exact reference containing precisely this statement with the required uniformity, should be supplied.
minor comments (5)
- [Section 4.2, proof of Lemma 4.6, Step 4] In Step 4 the integral I6 is written as the integral over E without a prior definition of the set E; it should presumably be S, and the integration should be over S intersected with the positive half-line in the region where the Hankel inversion formula is applied.
- [Section 4.2, Proposition 4.1 and Lemma 4.6] The definition I={[j,j+1] with j in Z} is used for sets S in the one-dimensional Hankel setting, where the underlying space is the positive half-line. Intersecting S with R+ would avoid ambiguity about negative intervals that play no role for functions on R+.
- [Section 3, Proposition 3.1, necessity part] The final displayed estimate in the necessity part, W(|ξ|) ≤ inf_n |ξ|^{n+1}/M_n ≤ C' divided by |Hνf(ξ)| times the product of |ξ_i|^{-n0}, is not immediate from the preceding product bounds. The cancellation between the infimum and the product estimate should be spelled out, or a supporting lemma from reference [20] quoted explicitly.
- [Section 2.2, Lemma 2.3] In the converse direction of the higher-dimensional Paley–Wiener theorem, the text asserts that the partial inverse h1(x1,z′) is entire in z′ and retains the same exponential type after applying the one-dimensional result for almost every z′. A short justification of the measurability in z′ and uniformity of the exponential type would improve the rigor of the iteration.
- [Section 4.3, Lemma 4.7] After rescaling by 2^{-mT}, the spectral support is only known to lie in the intersection of 2^{-mT}Y+[−2,2] with the positive half-line. The text should specify at which scale this expanded set is δ-regular and which value of h is used in Proposition 4.1 at the m-th step; otherwise the application of Proposition 4.1 is not immediate.
Circularity Check
No definitional circularity: the main FUP proof reduces to external Fourier FUP and BM-damping results, not to its own target, and only a minor non-load-bearing self-citation to [30] appears.
full rationale
The derivation of Theorem 1.4 is an external-lemma chain: PSH-BM and A-BM are imported from [7]; the translated Fourier FUP (Proposition 4.2) is asserted by modification of [3, Proposition 3.3] and [8, Proposition 3.5]; damping functions for regular sets (Lemma 4.4 and Remark 4.5) are deferred to [3, Lemma 3.1] and [8, Proposition 3.5]; and the Bessel-to-Fourier reduction in Lemma 4.6 follows [21]. None of these inputs contains the target Hankel FUP, and no parameter is fitted to the conclusion. The only self-citation is [30], which is used for background and in Remark 1.7 as an explicitly unsuccessful alternative; Theorem 1.3's proof does not depend on [30]'s theorem. The genuine weakness is that Remark 4.5 asserts, without proof, that translating and reflecting the centered construction gives uniform-in-eta centered dampers; if untrue, Proposition 4.1 and Lemma 4.7 fail. That is an omitted proof and a correctness gap, not a circular reduction: the asserted damper is an input from external sources, not the target inequality itself. Similarly, the mismatch between W in (4.17) and W^{1/2} in (4.22) is a technical error, not circularity. Hence score 2 reflects a minor, non-load-bearing self-citation and external-reliance concerns, with no significant circularity.
Assumptions & free parameters
assumptions (5)
- ad hoc to paper Existence of damping functions for delta-regular sets in the Fourier-Bessel setting (Lemma 4.4).
- domain assumption Translated sets Y-eta and their reflections remain delta-regular with the same constant C_R.
- domain assumption Fourier FUP for translated and reflected sets (Proposition 4.2).
- standard math Cohen's plurisubharmonic and analytic Beurling-Malliavin lemmas in dimension d.
- standard math Denjoy-Carleman characterization of quasi-analytic classes.
Cite this review
Pith. "Pith review of Fractal Uncertainty and Quantitative Uniqueness for the Fourier Bessel Transform." pith.science (2026). https://pith.science/paper/5YJMYMHA
@misc{pith2026260815126,
author = {Pith},
title = {Pith review of: Fractal Uncertainty and Quantitative Uniqueness for the Fourier Bessel Transform},
year = {2026},
howpublished = {\url{https://pith.science/paper/5YJMYMHA}},
note = {Machine review of arXiv:2608.15126}
}
abstract
We establish quantitative uniqueness and a fractal uncertainty principle for the Fourier Bessel transform. In arbitrary dimension, we prove a quantitative uniqueness estimate on relatively dense sets for functions whose Fourier Bessel transforms decay according to a quasi-analytic weight. In dimension one, if $X\subset[0,1]$ and $Y\subset[a,a+h^{-1}]$ are$\delta$-regular on the relevant scales, then, for $a\geq a_0h^{-1}$, \[ \operatorname{supp}\mathcal H_\nu f\subset Y \quad\Longrightarrow\quad \|\mathbf 1_Xf\|_{L^2_\nu} \leq Ch^\beta\|f\|_{L^2_\nu}. \] The lack of translation invariance prevents a direct application of the classical Fourier argument. We overcome this by constructing damping functions adapted to translated regular sets and combining Beurling Malliavin multipliers with large-argument Bessel asymptotics and a Bourgain Dyatlov multiscale iteration.
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