On vector measures with values in $\ell_\infty$

TL;DR

This paper investigates countably additive vector measures in ll_ty, revealing conditions for non-countably additive measures and establishing separability criteria for associated Banach lattices.

Contribution

It provides new insights into the structure of vector measures in ll_ty and characterizes when Banach lattices and measure spaces are separable.

Findings

Existence of non-countably additive ll_ty}-valued maps under certain conditions.

Separable Banach lattices with order continuous duals admit countable positively norming sets.

L_1(ll_ty)-spaces are separable if ll_ty}-valued measures are countably additive and their duals are order continuous.

Abstract

We study some aspects of countably additive vector measures with values in $\ell_\infty$ and the Banach lattices of real-valued functions that are integrable with respect to such a vector measure. On the one hand, we prove that if $W \subseteq \ell_\infty^*$ is a total set not containing sets equivalent to the canonical basis of $\ell_1(\mathfrak{c})$, then there is a non-countably additive $\ell_\infty$-valued map $\nu$ defined on a $\sigma$-algebra such that the composition $x^* \circ \nu$ is countably additive for every $x^*\in W$. On the other hand, we show that a Banach lattice $E$ is separable whenever it admits a countable positively norming set and both $E$ and $E^*$ are order continuous. As a consequence, if $\nu$ is a countably additive vector measure defined on a $\sigma$-algebra and taking values in a separable Banach space, then the space $L_1(\nu)$ is separable whenever $L_1(\nu)^*$ is order continuous.