On the Mackey problem for free abelian topological groups

TL;DR

This paper demonstrates that free abelian topological groups over certain non-discrete metrizable spaces lack a Mackey group topology, extending previous examples and highlighting limitations in their topological structure.

Contribution

It extends prior work by showing that free abelian topological groups over all non-discrete zero-dimensional metrizable spaces do not admit Mackey group topologies.

Findings

Free abelian topological groups over non-discrete zero-dimensional metrizable spaces lack Mackey topologies.

This extends previous examples from convergent sequences to broader classes of spaces.

All such groups over countable non-discrete metrizable spaces also lack Mackey topologies.

Abstract

Recently Au\ss enhofer and the author independently have shown that the free abelian topological group $A(\mathbf{s})$ over a convergent sequence $\mathbf{s}$ does not admit the strongest compatible locally quasi-convex group topology that gives the first example of a locally quasi-convex abelian group without a Mackey group topology. In this note we considerably extend this example by showing that the free abelian topological group $A(X)$ over a non-discrete zero-dimensional metrizable space $X$ does not have a Mackey group topology. In particular, for every countable non-discrete metrizable space $X$, the group $A(X)$ does not have a Mackey group topology.