English

Classes of barren extensions

Logic 2023-06-22 v3

Abstract

Henle, Mathias, and Woodin proved that, provided that ω(ω)ω\omega\rightarrow(\omega)^{\omega} holds in a model MM of ZF, then forcing with ([ω]ω,)([\omega]^{\omega},\subseteq^*) over MM adds no new sets of ordinals, thus earning the name a "barren" extension. Moreover, under an additional assumption, they proved that this generic extension preserves all strong partition cardinals. This forcing thus produces a model M[U]M[\mathcal{U}], where U\mathcal{U} is a Ramsey ultrafilter, with many properties of the original model MM. This begged the question of how important the Ramseyness of U\mathcal{U} is for these results. In this paper, we show that several classes of σ\sigma-closed forcings which generate non-Ramsey ultrafilters have the same properties. Such ultrafilters include Milliken-Taylor ultrafilters, a class of rapid p-points of Laflamme, kk-arrow p-points of Baumgartner and Taylor, and extensions to a class of ultrafilters constructed by Dobrinen, Mijares and Trujillo. Furthermore, the class of Boolean algebras P(ωα)/Finα\mathcal{P}(\omega^{\alpha})/\mathrm{Fin}^{\otimes \alpha}, 2α<ω12\le \alpha<\omega_1, forcing non-p-points also produce barren extensions.

Keywords

Cite

@article{arxiv.1911.06936,
  title  = {Classes of barren extensions},
  author = {Natasha Dobrinen and Daniel Hathaway},
  journal= {arXiv preprint arXiv:1911.06936},
  year   = {2023}
}

Comments

Accepted to JSL. A few revisions from the last posting

R2 v1 2026-06-23T12:17:45.656Z