Operators on the space of vector-valued totally measurable functions

AbstractLet L(X,Y) stand for the space of all bounded linear operators between real Banach spaces X and Y, and let Σ be a σ-algebra of sets. A bounded linear operator T from the Banach space B(Σ,X) of X-valued Σ-totally measurable functions to Y is said to be σ-smooth if ‖T(fn)‖Y→0 whenever a sequence of scalar functions (‖fn(⋅)‖X) is order convergent to 0 in B(Σ). It is shown that a bounded linear operator T:B(Σ,X)→Y is σ-smooth if and only if its representing measure m:Σ→L(X,Y) is variationally semi-regular, i.e., m˜(An)→0 as An↓∅ (here m˜(A) stands for the semivariation of m on A∈Σ). As an application, we show that the space Lσs(B(Σ,X),Y) of all σ-smooth operators from B(Σ,X) to Y provided with the strong operator topology is sequentially complete. We derive a Banach–Steinhaus type theorem for σ-smooth operators from B(Σ,X) to Y. Moreover, we characterize countable additivity of measures m:Σ→L(X,Y) in terms of continuity of the corresponding operators T:B(Σ,X)→Y