Discrete Analogoues in Harmonic Analysis: Maximally Monomially Modulated Singular Integrals Related to Carleson's Theorem

TL;DR

This paper proves boundedness of maximally monomially modulated discrete Hilbert transforms on or all p in a specific range, and establishes pointwise convergence of modulated ergodic Hilbert transforms for measure-preserving systems.

Contribution

It introduces and analyzes the boundedness of a new class of maximally modulated discrete Hilbert transforms related to monomials, extending prior work on singular integrals.

Findings

Boundedness of or all p in a specific range for the maximally monomially modulated discrete Hilbert transform.

Almost everywhere pointwise convergence of modulated ergodic Hilbert transforms as .

Extension of classical harmonic analysis results to monomial modulation cases.

Abstract

Motivated by Bourgain's work on pointwise ergodic theorems, and the work of Stein and Stein-Wainger on maximally modulated singular integrals without linear terms, we prove that the maximally monomially modulated discrete Hilbert transform, \[ \mathcal{C}_df(x) := \sup_\lambda \left| \sum_{m \neq 0} f(x-m) \frac{e^{2\pi i \lambda m^d}}{m} \right| \] is bounded on all $\ell^p, \ 2 - \frac{1}{d^2 + 1} < p < \infty$, for any $d \geq 2$. We also establish almost everywhere pointwise convergence of the modulated ergodic Hilbert transforms (as $\lambda \to 0$) \[ \sum_{m \neq 0} T^m f(x) \cdot \frac{e^{2\pi i \lambda m^d}}{m} \] for any measure-preserving system $(X,\mu,T)$, and any $f \in L^p(X), \ 2 - \frac{1}{d^2 +1} < p < \infty$.