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arxiv: 2411.01674 · v1 · submitted 2024-11-03 · 🧮 math.CV

Bohr type inequality for certain integral operators and Fourier transform on shifted disks

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classification 🧮 math.CV
keywords Bohr inequalityCesàro operatorBernardi integral operatordiscrete Fourier transformshifted disksbounded analytic functionsgeometric function theory
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The pith

Cesàro, Bernardi integral and discrete Fourier operators satisfy sharp Bohr-type inequalities for bounded analytic functions on shifted disks Ω_γ.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper derives sharp Bohr type inequalities for the Cesàro operator, the Bernardi integral operator, and the discrete Fourier transform applied to bounded analytic functions defined on shifted disks Ω_γ. These inequalities bound the sums of the absolute values of the Taylor coefficients of the resulting functions. A reader would care because the bounds are claimed to be best possible and extend the classical Bohr phenomenon from the unit disk to these translated circular domains for every γ in [0,1).

Core claim

In this paper, we derive the sharp Bohr type inequality for the Cesàro operator, Bernardi integral operator, and discrete Fourier transform acting on the class of bounded analytic functions defined on shifted disks Ω_γ for γ∈[0,1).

What carries the argument

The shifted disks Ω_γ = {z : |z + γ/(1-γ)| < 1/(1-γ)} for γ ∈ [0,1), the domain on which the bounded analytic functions live and to which the three operators are applied.

Load-bearing premise

The bounded analytic functions on Ω_γ form a class on which the Cesàro, Bernardi, and discrete Fourier operators produce functions whose coefficient sums satisfy the stated sharp Bohr-type bounds.

What would settle it

Exhibit one bounded analytic function on a specific Ω_γ whose image under the Cesàro operator (or either of the other two) has coefficient sum exceeding the claimed sharp bound at the relevant radius.

Figures

Figures reproduced from arXiv: 2411.01674 by Rajib Mandal, Raju Biswas, Vasudevarao Allu.

Figure 1
Figure 1. Figure 1: The graphs of Cγ when γ = 0, 0.2, 0.4, 0.5, 0.7 Besides the Bohr radius, there is another concept known as the Rogosinski radius [30, 42]. It is described as follows: Let SN (z) := PN−1 n=0 anz n be the partial sum of f ∈ B(D) defined by f(z) = P∞ n=0 anz n . Then, |SN (z)| < 1 for all N ≥ 1 in the disk |z| < 1/2. Here 1/2 is sharp, known as Rogosinski radius. Kayumov and Ponnusamy [20] have introduced the… view at source ↗
Figure 2
Figure 2. Figure 2: The graph of −2 (1/(1 − ρ) + log(1 − ρ)/ρ) for ρ ∈ [0, 1) Therefore, ∂ ∂aφ1(a, ρ) is a monotonically decreasing function of a ∈ [0, 1] and it follows that ∂ ∂aφ1(a, ρ) ≥ ∂ ∂aφ1(1, ρ) = −2ρ − 3(1 − ρ) log(1 − ρ) (1 − ρ)ρ ≥ 0 for ρ ≤ ρ0, where ρ0(≈ 0.533589) is the positive root of the equation 3(1 − ρ) log(1 − ρ) + 2ρ = 0, as illustrated in [PITH_FULL_IMAGE:figures/full_fig_p007_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: The graph of 3(1 − ρ) log(1 − ρ) + 2ρ for ρ ∈ [0, 1) Therefore φ1(a, ρ) is a monotonically increasing function of a ∈ [0, 1] and it follows that φ1(a, ρ) ≤ φ1(1, ρ) = − 1 ρ log(1 − ρ) = 1 ρ log 1 (1 − ρ) for ρ ≤ ρ0. To prove the sharpness of the result, we consider the function f1(z) in Ωγ such that f1 = ψ ◦ Φ1, where Φ1 : Ωγ → D defined by Φ1(z) = γ + (1 − γ)z and ψ : D → D defined by ψ(z) = (a − z)/(1 − … view at source ↗
read the original abstract

In this paper, we derive the sharp Bohr type inequality for the Ces\'aro operator, Bernardi integral operator, and discrete Fourier transform acting on the class of bounded analytic functions defined on shifted disks \beas \Omega_{\gamma}=\left\{z\in\mathbb{C}:\left|z+\frac{\gamma}{1-\gamma}\right|<\frac{1}{1-\gamma}\right\}\quad\text{for}\quad\gamma\in[0,1).\eeas

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 2 minor

Summary. The manuscript derives sharp Bohr-type inequalities for the Cesàro operator, Bernardi integral operator, and discrete Fourier transform acting on the class of analytic functions f with |f| ≤ 1 on the shifted disks Ω_γ = {z : |z + γ/(1-γ)| < 1/(1-γ)} for γ ∈ [0,1).

Significance. If the sharpness arguments are valid for the restricted class of functions bounded on the full Ω_γ (a proper superset of the unit disk), the results would extend classical Bohr inequalities to a parameterized family of domains and provide explicit constants for these specific operators. The work supplies explicit derivations and sharpness claims for three operators.

major comments (1)
  1. [proofs of the main theorems (Cesàro, Bernardi, and Fourier cases)] The central sharpness claims (for all three operators) rest on extremal functions that must remain in the class |f|≤1 on all of Ω_γ. Because Ω_γ properly contains the open unit disk and the class is therefore a strict subclass of H^∞(D), standard extremals (Möbius maps or their compositions) used for the unit-disk case may violate |f|≤1 at points of Ω_γ outside D. The manuscript must exhibit or verify admissible extremals that attain the stated constants inside Ω_γ; otherwise the constants are not sharp for the stated class. This issue is load-bearing for every “sharp” statement in the main theorems.
minor comments (2)
  1. [abstract] The equation defining Ω_γ in the abstract uses display math that could be typeset more cleanly for readability.
  2. [preliminaries] A brief remark on how the discrete Fourier transform is defined on the coefficient sequence of functions analytic in Ω_γ would clarify the operator for readers.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the careful reading of the manuscript and for highlighting the critical issue with the sharpness arguments. We address the concern point by point below.

read point-by-point responses
  1. Referee: [proofs of the main theorems (Cesàro, Bernardi, and Fourier cases)] The central sharpness claims (for all three operators) rest on extremal functions that must remain in the class |f|≤1 on all of Ω_γ. Because Ω_γ properly contains the open unit disk and the class is therefore a strict subclass of H^∞(D), standard extremals (Möbius maps or their compositions) used for the unit-disk case may violate |f|≤1 at points of Ω_γ outside D. The manuscript must exhibit or verify admissible extremals that attain the stated constants inside Ω_γ; otherwise the constants are not sharp for the stated class. This issue is load-bearing for every “sharp” statement in the main theorems.

    Authors: We agree with the referee that the sharpness claims require extremal functions belonging to the class |f|≤1 on the entire domain Ω_γ, not merely on the unit disk. The manuscript currently invokes standard extremals from the classical unit-disk setting without explicitly verifying that these functions remain bounded by 1 throughout Ω_γ. This is a substantive gap. In the revised version we will either (i) construct or identify admissible extremals that attain the claimed constants while satisfying |f|≤1 on all of Ω_γ, or (ii) qualify the sharpness statements if no such functions exist for the given operators. The revision will cover the Cesàro, Bernardi, and discrete Fourier cases uniformly. revision: yes

Circularity Check

0 steps flagged

No circularity in derivation chain

full rationale

The abstract claims derivation of sharp Bohr-type inequalities for Cesàro, Bernardi, and discrete Fourier operators on bounded analytic functions over Ω_γ. No equations, coefficient relations, fitted parameters, or self-citations appear in the provided text that reduce any claimed prediction or bound to an input by construction. The domain and class definitions are independent of the target inequalities, and no load-bearing step is shown to collapse via self-definition, renaming, or imported uniqueness. The skeptic concern addresses whether sharpness holds for the restricted class, which is a correctness question outside circularity analysis.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Abstract supplies no information on free parameters, background axioms, or new postulated entities.

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Works this paper leans on

46 extracted references · 46 canonical work pages · 1 internal anchor

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