Published online by Cambridge University Press: 20 November 2018
Let $L(X)$ be the space of bounded linear operators on the Banach space
$X$. We study the strict singularity and cosingularity of the two-sided multiplication operators
$S\,\mapsto \,ASB$ on
$L(X)$, where
$A,\,B\,\in \,L(X)$ are fixed bounded operators and
$X$ is a classical Banach space. Let
$1\,<\,p\,<\,\infty $ and
$p\,\ne \,2$. Our main result establishes that the multiplication
$S\,\mapsto \,ASB$ is strictly singular on
$L\left( {{L}^{p}}\left( 0,\,1 \right) \right)$ if and only if the non-zero operators
$A,\,B\,\in \,L\left( {{L}^{p}}\left( 0,\,1 \right) \right)$ are strictly singular. We also discuss the case where
$X$ is a
${\mathcal{L}^{1}}-$ or a
${{\mathcal{L}}^{\infty }}-$space, as well as several other relevant examples.