Essential norms of fractional Volterra-type operators

Abstract

Given a radial doubling weight $μ$ on the unit disk $\mathbb{D}$ and $f(z)=\sum_{n=0}^\infty \hat{f}(n)z^n\in\mathcal{H}(\mathbb{D})$, the fractional derivative of $f$ induced by $μ$ is $$ D^μ(f)(z) = \sum_{n=0}^\infty \frac{\hat{f}(n)}{μ_{2n+1}}z^n, $$ where $μ_{2n+1}=\int_0^1 r^{2n+1}μ(r)\,dr$ are the odd moments of $μ$. The fractional integral of $f$ induced by $μ$ is $I^μ(f)(z)=\sum_{n=0}^\infty μ_{2n+1}\hat{f}(n)z^n$. We study the fractional Volterra-type operator $$ V_{μ,g}(f)(z)=I^μ(f\cdot D^μ(g))(z),\quad f\in\mathcal{H}(\mathbb{D}), $$ with symbol $g\in\mathcal{H}(\mathbb{D})$, introduced by Bellavita, Moreno, Nikolaidis and Peláez. First, we estimate the essential norm of $V_{μ,g}$ acting on $H^p$ and $A^p_α$. Later, we study the same questions for $V_{μ,g}:H^p\to H^q$ and $V_{μ,g}:A^p_α\to A^q_α$, characterizing their boundedness and compactness and estimating their essential norms for all $0<p,q<\infty$.