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

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, \[ \mathcal{C}_df(x) := \sup_λ\left| \sum_{m \neq 0} f(x-m) \frac{e^{2πi λm^d}}{m} \right| \] 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 $λ\to 0$) \[ \sum_{m \neq 0} T^m f(x) \cdot \frac{e^{2πi λm^d}}{m} \] for any measure-preserving system $(X,μ,T)$, and any $f \in L^p(X), \ 2 - \frac{1}{d^2 +1} < p < \infty$.