Bergman-Bourgain-Brezis-type Inequality

TL;DR

This paper establishes a fractional version of the Bourgain-Brezis inequality in one dimension, linking the membership of holomorphic functions in the Bergman space to boundary behavior in specific function spaces.

Contribution

It introduces a fractional inequality in 1-D and shows its equivalence to holomorphic functions being in the Bergman space, with potential extensions to higher dimensions.

Findings

Fractional Bourgain-Brezis inequality in 1-D proved.

Characterization of Bergman space functions via boundary norms.

Exploration of generalizations to higher-dimensional tori.

Abstract

In this note, we prove a fractional version in $1$-D of the Bourgain-Brezis inequality \cite{bourgain1}. We show that such an inequality is equivalent to the fact that a holomorphic function $f\colon\D\to\C$ belongs to the Bergman space ${\mathcal{A}}^2(\D)$, namely $f\in L^2(\D)$, if and only if $$\|f\|_{ L^1+ {H}^{-1/2}(S^1)}:=\limsup_{r\to 1^-}\|f(re^{i\theta})\|_{ L^1+ {H}^{-1/2}(S^1)}<+\infty.$$ Possible generalisations to the higher-dimensional torus are explored.