Disjointness preserving operators on Köthe-Banach spaces

Abstract

A well-known result of Abramovich says that if $E$, $F$ are rearrangement invariant Banach spaces on a finite atomless measure space such that $E$ has an absolutely continuous norm and $E\not\subseteq F$, then there are no nonzero disjointness preserving bounded linear operators $T \colon E\to F$. We obtain an analogue of this result in the setting of general Köthe-Banach spaces. Specifically, we identify a sufficient condition on Köthe-Banach spaces $E$, $F$ on finite atomless measure spaces that implies that there are no nonzero disjointness preserving bounded linear operators $T \colon E\to F$. Consequently, by a representation theorem for regular operators due to O.~Maslyuchenko, Mykhaylyuk and the second named author, this condition implies that every regular linear operator $T \colon E\to F$ is narrow. As an application, we obtain that if $1\le \max\{p_1,p_2\}< \min\{ r_1, r_2\}\le \infty$, then every regular linear operator $T \colon L_{p_1}(L_{p_2}) \to L_{r_1}(L_{r_2})$ is narrow. The latter may be seen as an analogue of the classical Pitt compactness theorem.