Bohr radius for Banach spaces on simply connected domains

TL;DR

This paper investigates the Bohr radius for bounded analytic functions from simply connected domains into Banach spaces, establishing inequalities and exploring the case for Hilbert spaces and specific operators.

Contribution

It introduces a generalized Bohr radius for Banach space-valued functions and extends classical inequalities to operator-valued Cesáro and Bernardi operators.

Findings

Defined a new Bohr radius $R_{p,q,}$ for Banach space-valued functions.

Established bounds and properties of the Bohr radius in various Banach spaces.

Proved Bohr inequalities for operator-valued Cesáro and Bernardi operators.

Abstract

Let $H^{\infty}(\Omega,X)$ be the space of bounded analytic functions $f(z)=\sum_{n=0}^{\infty} x_{n}z^{n}$ from a proper simply connected domain $\Omega$ containing the unit disk $\mathbb{D}:=\{z\in \mathbb{C}:|z|<1\}$ into a complex Banach space $X$ with $\norm{f}_{H^{\infty}(\Omega,X)} \leq 1$. Let $\phi=\{\phi_{n}(r)\}_{n=0}^{\infty}$ with $\phi_{0}(r)\leq 1$ such that $\sum_{n=0}^{\infty} \phi_{n}(r)$ converges locally uniformly with respect to $r \in [0,1)$. For $1\leq p,q<\infty$, we denote \begin{equation*} R_{p,q,\phi}(f,\Omega,X)= \sup \left\{r \geq 0: \norm{x_{0}}^p \phi_{0}(r) + \left(\sum_{n=1}^{\infty} \norm{x_{n}}\phi_{n}(r)\right)^q \leq \phi_{0}(r)\right\} \end{equation*} and define the Bohr radius associated with $\phi$ by $$R_{p,q,\phi}(\Omega,X)=\inf \left\{R_{p,q,\phi}(f,\Omega,X): \norm{f}_{H^{\infty}(\Omega,X)} \leq 1\right\}.$$ In this article, we extensively study the Bohr radius $R_{p,q,\phi}(\Omega,X)$, when $X$ is an arbitrary Banach space and $X$ is certain Hilbert space. Furthermore, we establish the Bohr inequality for the operator-valued Ces\'{a}ro operator and Bernardi operator.