English

Indestructibility of some compactness principles over models of PFA

Logic 2022-08-05 v1

Abstract

We show that PFA\mathsf{PFA} (Proper Forcing Axiom) implies that adding any number of Cohen subsets of ω\omega will not add an ω2\omega_2-Aronszajn tree or a weak ω1\omega_1-Kurepa tree, and moreover no σ\sigma-centered forcing can add a weak ω1\omega_1-Kurepa tree (a tree of height and size ω1\omega_1 with at least ω2\omega_2 cofinal branches). This partially answers an open problem whether ccc forcings can add ω2\omega_2-Aronszajn or ω1\omega_1-Kurepa trees. We actually prove more: We show that a consequence of PFA\mathsf{PFA}, namely the guessing model principle, GMP\mathsf{GMP}, which is equivalent to the ineffable slender tree property, ISP\mathsf{ISP}, is preserved by adding any number of Cohen subsets of ω\omega. And moreover, GMP\mathsf{GMP} implies that no σ\sigma-centered forcing can add a weak ω1\omega_1-Kurepa tree. For more generality, we study the principle GMP\mathsf{GMP} at an arbitrary regular cardinal κ=κ<κ\kappa = \kappa^{<\kappa} (we denote this principle GMPκ++\mathsf{GMP}_{\kappa^{++}}), and as an application we show that there is a model in which there are no weak ω+1\aleph_{\omega+1}-Kurepa trees and no ω+2\aleph_{\omega+2}-Aronszajn trees.

Keywords

Cite

@article{arxiv.2208.02684,
  title  = {Indestructibility of some compactness principles over models of PFA},
  author = {Radek Honzik and Chris Lambie-Hanson and Šárka Stejskalová},
  journal= {arXiv preprint arXiv:2208.02684},
  year   = {2022}
}

Comments

18 pages