English

Topological groups with tractable minimal dynamics

Dynamical Systems 2025-09-11 v2 Logic

Abstract

A Polish group GG has the generic point property if any minimal GG-flow admits a comeager orbit, or equivalently if the universal minimal flow (UMF) does. The class GPP\mathsf{GPP} of such Polish groups is a proper extension of the class PCMD\sf{PCMD} of Polish groups with metrizable UMF. Motivated by analogous results for PCMD\mathsf{PCMD}, we define and explore a robust generalization of GPP\sf{GPP} which makes sense for all topological groups, thus defining the class TMD\mathsf{TMD} of topological groups with tractable minimal dynamics. These characterizations yield novel results even for GPP\mathsf{GPP}; for instance, a Polish group is in GPP\mathsf{GPP} iff its UMF has no points of first countability. Motivated by work of Kechris, Pestov, and Todor\v{c}evi\'c that connects topological dynamics and structural Ramsey theory, we state and prove an abstract KPT correspondence which characterizes the class TMD\mathsf{TMD} and shows that TMD\mathsf{TMD} is Δ1\Delta_1 in the L\'evy hierarchy. We then develop set-theoretic methods which allow us to apply forcing and absoluteness arguments to generalize numerous results about GPP\mathsf{GPP} to all of TMD\mathsf{TMD}. We also apply these new set-theoretic methods to first generalize parts of Glasner's structure theorem for minimal, metrizable tame flows to the non-metrizable setting, and then to prove the revised Newelski conjecture regarding definable NIP groups. We conclude by discussing some tantalizing connections between definable NIP groups and TMD\mathsf{TMD} groups.

Keywords

Cite

@article{arxiv.2412.05659,
  title  = {Topological groups with tractable minimal dynamics},
  author = {Gianluca Basso and Andy Zucker},
  journal= {arXiv preprint arXiv:2412.05659},
  year   = {2025}
}

Comments

112 pages; major expansion of version 1

R2 v1 2026-06-28T20:26:35.726Z