Sur quelques extensions au cadre Banachique de la notion d'opérateur de Hilbert-Schmidt

Abstract

In this work we discuss several ways to extend to the context of Banach spaces the notion of Hilbert-Schmidt operators: $p$-summing operators, $\gamma$-summing or $\gamma$-radonifying operators, weakly $\ast 1$-nuclear operators and classes of operators defined via factorization properties. We introduce the class $P{S}_2(E;F)$ of pre-Hilbert-Schmidt operators as the class of all operators $u:E\to F$ such that $w\circ u\circ v$ is Hilbert-Schmidt for every bounded operator $v:H_1\to E$ and every bounded operator $w:F\to H_2$, where $H_1$ et $H_2$ are Hilbert spaces. Besides the trivial case where one of the spaces $E$ or $F$ is a "Hilbert-Schmidt space", this space seems to have been described only in the easy situation where one of the spaces $E$ or $F$ is a Hilbert space.

18 pages, in French