English

Generalized cardinal invariants for an inaccessible $\kappa$ with compactness at $\kappa^{++}$

Logic 2025-04-28 v2

Abstract

We show that if the existence of a supercompact cardinal κ\kappa with a weakly compact cardinal λ\lambda above κ\kappa is consistent, then the following are consistent as well (where t(κ)\mathfrak{t}(\kappa) and u(κ)\mathfrak{u}(\kappa) are the tower number and the ultrafilter number, respectively): (i) There is an inaccessible cardinal κ\kappa such that κ+<t(κ)=u(κ)<2κ\kappa^+ < \mathfrak{t}(\kappa)= \mathfrak{u}(\kappa)< 2^\kappa and SR(κ++)SR(\kappa^{++}) hold, and (ii) There is an inaccessible cardinal κ\kappa such that κ+=t(κ)<u(κ)<2κ\kappa^+ = \mathfrak{t}(\kappa) < \mathfrak{u}(\kappa)< 2^\kappa and SR(κ++),TP(κ++)SR(\kappa^{++}), TP(\kappa^{++}) and ¬wKH(κ+)\neg wKH(\kappa^+) hold. The cardinals u(κ)\mathfrak{u}(\kappa) and 2κ2^\kappa can have any reasonable values in these models. We obtain these results by combining the forcing construction from Brooke-Taylor, Fischer, Friedman and Montoya with the Mitchell forcing and with (new and old) indestructibility results for compactness principles. Apart from u(κ)\mathfrak{u}(\kappa) and t(κ)\mathfrak{t}(\kappa) we also compute the values of b(κ)\mathfrak{b}(\kappa), d(κ)\mathfrak{d}(\kappa), s(κ)\mathfrak{s}(\kappa), r(κ)\mathfrak{r}(\kappa), a(κ)\mathfrak{a}(\kappa), cov(Mκ)\mathrm{cov}(M_\kappa), add(Mκ)\mathrm{add}(M_\kappa), non(Mκ)\mathrm{non}(M_\kappa), cof(Mκ)\mathrm{cof}(M_\kappa) which will all be equal to u(κ)\mathfrak{u}(\kappa). In (ii), we compute p(κ)=t(κ)=κ+\mathfrak{p}(\kappa) = \mathfrak{t}(\kappa) = \kappa^+ by observing that the κ+\kappa^+-distributive quotient of the Mitchell forcing adds a tower of size κ+\kappa^+. Finally, we observe that (i) and (ii) hold also for the traditional invariants on κ=ω\kappa = \omega, using Mitchell forcing up to a weakly compact cardinal; in this case we also obtain the disjoint stationary sequence property DSS(ω2)DSS(\omega_2), which implies the negation of the approachability property ¬AP(ω2)\neg AP(\omega_2).

Keywords

Cite

@article{arxiv.2308.13478,
  title  = {Generalized cardinal invariants for an inaccessible $\kappa$ with compactness at $\kappa^{++}$},
  author = {Radek Honzik and Sarka Stejskalova},
  journal= {arXiv preprint arXiv:2308.13478},
  year   = {2025}
}

Comments

27 pages, to appear in Archive for Mathematical Logic. A substantial revision of the previous version with more details (also regarding the principle DSS)