Countable dense homogeneity in powers of zero-dimensional definable spaces

TL;DR

The paper investigates conditions under which powers of zero-dimensional definable spaces are countably dense homogeneous, establishing equivalences for coanalytic subspaces of Cantor space and constructing non-Polish examples with this property.

Contribution

It proves that for coanalytic subspaces of Cantor space, countable dense homogeneity of their powers is equivalent to being Polish, and constructs a non-Polish example with this property in ZFC.

Findings

Countable dense homogeneity of $X^ ext{omega}$ is equivalent to $X$ being Polish for coanalytic subspaces.

Constructed a non-Polish subspace $X$ of $2^ ext{omega}$ with $X^ ext{omega}$ countable dense homogeneous in ZFC.

Showed that if every countable subset of a space is contained in a Polish subspace, then its power is countable dense homogeneous.

Abstract

We show that, for a coanalytic subspace $X$ of $2^\omega$, the countable dense homogeneity of $X^\omega$ is equivalent to $X$ being Polish. This strengthens a result of Hru\v{s}\'ak and Zamora Avil\'es. Then, inspired by results of Hern\'andez-Guti\'errez, Hru\v{s}\'ak and van Mill, using a technique of Medvedev, we construct a non-Polish subspace $X$ of $2^\omega$ such that $X^\omega$ is countable dense homogeneous. This gives the first $\mathsf{ZFC}$ answer to a question of Hru\v{s}\'ak and Zamora Avil\'es. Furthermore, since our example is consistently analytic, the equivalence result mentioned above is sharp. Our results also answer a question of Medini and Milovich. Finally, we show that if every countable subset of a zero-dimensional separable metrizable space $X$ is included in a Polish subspace of $X$ then $X^\omega$ is countable dense homogeneous.