Generalized Hilbert Operator Acting on Hardy Spaces

TL;DR

This paper investigates the boundedness, compactness, and essential norm of a generalized Hilbert operator induced by a measure on Hardy spaces, extending classical results and characterizing measures for operator properties.

Contribution

It characterizes measures for which the generalized Hilbert operator is bounded or compact on Hardy spaces and computes its essential norm, extending previous operator theory results.

Findings

Characterization of measures for boundedness of the operator.

Criteria for compactness of the operator.

Explicit computation of the operator's essential norm.

Abstract

Let $\alpha>0$ and $\mu$ be a positive Borel measure on the interval $[0,1)$. The Hankel matrix $\mathcal{H}_{\mu,\alpha}=(\mu_{n,k,\alpha})_{n,k\ge0}$ with entries $\mu_{n,k,\alpha}=\int_{[0,1)}^{}\frac{\Gamma(n+\alpha)}{\Gamma(n+1)\Gamma(\alpha)}t^{n+k}d\mu(t)$, induces, formally, the generalized-Hilbert operator as $$ \mathcal{H}_{\mu,\alpha}\left ( f \right ) \left ( z \right ) =\sum_{n=0}^{\infty} \left (\sum_{k=0}^{\infty} \mu_{n,k,\alpha}a_k \right )z^n,z\in\mathbb{D} $$ where $f(z)={\textstyle \sum_{k=0}^{\infty }} a_kz^k$ is an analytic function in $\mathbb{D}$. This article is devoted study the measures $\mu$ for which $\mathcal{H}_{\mu,\alpha }$ is a bounded(resp., compact) operator from $H^p(0<p\le1)$ into $H^p(1\le q<\infty)$. Then, we also study the analogous problem in the Hardy spaces $H^p(1\le p\le2)$. Finally, we obtain the essential norm of $\mathcal{H}_{\mu,\alpha}$ from $H^p(0<p\le1)$ into $H^p(1\le q<\infty)$.