A theory of complex oscillatory integrals: A case study

TL;DR

This paper develops a new theoretical framework for analyzing oscillatory integrals with complex phases, addressing the lack of scale-invariant bounds in the complex setting and proposing methods to establish such bounds under specific conditions.

Contribution

It introduces a novel approach to establish scale-invariant bounds for complex oscillatory integrals, which are not generally available in the complex case.

Findings

Identified limitations of scale-invariant bounds in complex oscillatory integrals.

Developed a new perspective to locate bounds in less general settings.

Provided theoretical tools for future analysis of complex oscillatory integrals.

Abstract

In this paper we develop a theory for oscillatory integrals with complex phases. When $f:{\mathbb C}^n \to {\mathbb C}$, we evaluate this phase function on the basic character ${\rm e}(z) := e^{2\pi i x} e^{2\pi i y}$ of ${\mathbb C} \simeq {\mathbb R}^2$ (here $z = x+iy \in {\mathbb C}$ or $z = (x,y) \in {\mathbb R}^2$) and consider oscillatory integrals of the form $$ I \ = \ \int_{{\mathbb C}^n} {\rm e}(f({\underline{z}})) \, \phi({\underline{z}}) \, d{\underline{z}} $$ where $\phi \in C^{\infty}_c({\mathbb C}^n)$. Unfortunately basic scale-invariant bounds for the oscillatory integrals $I$ do not hold in the generality that they do in the real setting. Our main effort is to develop a perspective and arguments to locate scale-invariant bounds in (necessarily) less generality than we are accustomed to in the real setting.