Discrete Ultrafilters and Homogeneity of Product Spaces

Abstract

An ultrafilter $p$ on $ω$ is said to be discrete if, given any function $f\colon ω\to X$ to any completely regular Hausdorff space, there is an $A \in p$ such that $f(A)$ is discrete. Basic properties of discrete ultrafilters are studied. Three intermediate classes of spaces $\mathscr R_1 \subset \mathscr R_2 \subset \mathscr R_3$ between the class of $F$-spaces and the class of van~Douwen's $βω$-spaces are introduced. It is proved that no product of infinite compact $\mathscr R_2$-spaces is homogeneous; moreover, under the assumption $\mathfrak d =\mathfrak c$, no product of $βω$-spaces is homogeneous.