Power-norms based on Hilbert $C^*$-modules

Abstract

Suppose that $\mathscr{E}$ and $\mathscr{F}$ are Hilbert $C^*$-modules. We present a power-norm $\left(\left\|\cdot\right\|^{\mathscr{E}}_n:n\in\mathbb{N}\right)$ based on $\mathscr{E}$ and obtain some of its fundamental properties. We introduce a new definition of the absolutely $(2,2)$-summing operators from $\mathscr{E}$ to $\mathscr{F}$, and denote the set of such operators by $\tildeΠ_2(\mathscr{E},\mathscr{F})$ with the convention $\tildeΠ_2(\mathscr{E})=\tildeΠ_2(\mathscr{E},\mathscr{E})$. It is known that the class of all Hilbert--Schmidt operators on a Hilbert space $\mathscr{H}$ is the same as the space $\tildeΠ_2(\mathscr{H})$. We show that the class of Hilbert--Schmidt operators introduced by Frank and Larson coincides with the space $\tildeΠ_2(\mathscr{E})$ for a countably generated Hilbert $C^*$-module $\mathscr{E}$ over a unital commutative $C^*$-algebra. These results motivate us to investigate the properties of the space $\tildeΠ_2(\mathscr{E},\mathscr{F})$.