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This is a question from MSE which has not received any attention so far.

Let $X$ be a Banach space with norm dual $X'$. (I am mostly interested in the case $X = \ell^1$.) For a linear mapping $T : X \to X$ denote by $T' : X' \to X'$, $(T'f)(x) := f(Tx)$ its adjoint. Denote by $B(X)$ the space of bounded operators on $X$ and by $L_{w^*}(X')$ the space of weakly$^*$-continuous operators on $X'$. Then $T \in B(X)$ iff $T' \in L_{w^*}(X')$. Moreover, any $S \in L_{w^*}(X')$ is of the form $S = T'$ for some $T \in B(X)$ (see here). Hence, we can identify $B(X) = L_{w^*}(X')$ as vector spaces.

On $B(X)$ we can consider the operator norm topology, the strong operator topology (SOT) and the weak operator topology (WOT). The above identification $B(X) = L_{w^*}(X')$ provides corresponding topologies on $L_{w^*}(X')$.

Now $L_{w^*}(X')$ is a linear subspace of $B(X')$. On $B(X')$ we can also consider these three types of topologies. Are the mentioned topologies on $L_{w^*}(X')$ (coming from $B(X)$) related in some way to these (or other familiar) topologies on $B(X')$? What about the special case of $X = \ell^1$ (with $X' = \ell^\infty$)?

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    $\begingroup$ It should be easy to prove that the operator norms are the same, that the SOT from $B(X')$ is finer than SOT from $B(X)$, and that the WOT from $B(X')$ is finer than WOT from $B(X)$. On $B(X')$ you have the topology of pointwise weak$^*$-convergence generated by the seminorm $\|S\|_{x',x}=|S(x')(x)|$ for $x'\in X'$ and $x\in X$. These seminorms induce the WOT on $B(X)$. $\endgroup$ Apr 24, 2018 at 13:51
  • $\begingroup$ @JochenWengenroth Thank you for the hint. It is indeed not hard to see when writing down the definitions and recalling the fact that for each $x \neq 0$ there is $x' \in X'$ with $\lVert x' \rVert = 1$ such that $\lVert x \rVert = x'(x)$. $\endgroup$
    – yada
    Apr 30, 2018 at 7:30

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