Dense-separable groups and its applications in $d$-independence

TL;DR

This paper investigates dense-separable topological groups, establishing their properties, characterizations, and applications in $d$-independent structures, including conditions for metrizability and $d$-independence in various classes of groups.

Contribution

It introduces and analyzes the concept of dense-separable topological groups, providing new characterizations, properties, and applications in $d$-independent groups, especially relating to metrizability and subgroup separability.

Findings

Separable spaces with countable tightness are dense-separable.

Certain classes of abelian groups are dense-subgroup-separable iff they are metrizable.

Conditions under which dense-subgroup-separable groups are $d$-independent.

Abstract

A topological space is called {\it dense-separable} if each dense subset of its is separable. Therefore, each dense-separable space is separable. We establish some basic properties of dense-separable topological groups. We prove that each separable space with a countable tightness is dense-separable, and give a dense-separable topological group which is not hereditarily separable. We also prove that, for a Hausdorff locally compact group , it is locally dense-separable iff it is metrizable. Moreover, we study dense-subgroup-separable topological groups. We prove that, for each compact torsion (or divisible, or torsion-free, or totally disconnected) abelian group, it is dense-subgroup-separable iff it is dense-separable iff it is metrizable. Finally, we discuss some applications in $d$-independent topological groups and related structures. We prove that each regular dense-subgroup-separable abelian semitopological group with $r_{0}(G)\geq\mathfrak{c}$ is $d$-independent. We also prove that, for each regular dense-subgroup-separable bounded paratopological abelian group $G$ with $|G|>1$, it is $d$-independent iff it is a nontrivial $M$-group iff each nontrivial primary component $G_{p}$ of $G$ is $d$-independent. Apply this result, we prove that a separable metrizable almost torsion-free paratopological abelian group $G$ with $|G|=\mathfrak{c}$ is $d$-independent. Further, we prove that each dense-subgroup-separable MAP abelian group with a nontrivial connected component is also $d$-independent.