Group topologies on groups of bi-absolutely continuous homeomorphisms (2401.00790v1)

Abstract: The group of homeomorphisms of the closed interval that are orientation preserving, absolutely continuous and have an absolutely continuous inverse was shown by Solecki to admit a natural Polish group topology $\tau_{ac}$. We observe that, more generally, under some conditions on a compact space endowed with a finite Borel measure an analogous Polish group topology can be defined on the subgroup of the homeomorphism group which push forward the measure to another one with which it is mutually absolutely continuous. We use a probabilistic argument involving approximations by supmartingale processes to show that in many cases there is no group topology between $\tau_{ac}$ and the restriction $\tau_{co}$ of the compact-open topology. This applies, in particular, to any compact topological manifold equipped with an Oxtoby-Ulam measure and to the Cantor space endowed with some natural Borel measures. In fact, we show that in such cases any separable group topology strictly finer than $\tau_{co}$ has to be also finer than $\tau_{ac}$. For one-dimensional manifolds well-known arguments show that the compact-open topology is a minimum Hausdroff group topology on the group, which implies that $\tau_{co}$ and $\tau_{ac}$ are the only Hausdorff group topologies coarser than $\tau_{ac}$. We also show that while Solecki's example is not Roelcke precompact, the group of bi-absolutely continuous homeomorphisms of the Cantor space endowed with the measure given by the Fr\"aiss\'e limit of the class of measured boolean algebras with rational probability measures is Roelcke precompact.