Sharp variation-norm estimates for oscillatory integrals related to Carleson's theorem

TL;DR

This paper establishes sharp variation-norm bounds for oscillatory integrals related to Carleson's theorem, with implications for discrete and ergodic theory, using advanced harmonic analysis techniques.

Contribution

It provides the first sharp variation-norm estimates for these integrals, extending known bounds to endpoint cases and improving local smoothing estimates in higher dimensions.

Findings

Proved sharp variation-norm bounds for oscillatory integrals.

Extended local smoothing estimates to higher dimensions using Bourgain-Guth iteration.

Improved the range of exponents for local smoothing in dimensions n ≥ 4.

Abstract

We prove variation-norm estimates for certain oscillatory integrals related to Carleson's theorem. Bounds for the corresponding maximal operators were first proven by Stein and Wainger. Our estimates are sharp in the range of exponents, up to endpoints. Such variation-norm estimates have applications to discrete analogues and ergodic theory. The proof relies on square function estimates for Schr\"odinger-like equations due to Lee, Rogers and Seeger. In dimension one, our proof additionally relies on a local smoothing estimate. Though the known endpoint local smoothing estimate by Rogers and Seeger is more than sufficient for our purpose, we also give a proof of certain local smoothing estimates using Bourgain-Guth iteration and the Bourgain-Demeter $\ell^2$ decoupling theorem. This may be of independent interest, because it improves the previously known range of exponents for spatial dimensions $n \ge 4$.