English

AD$^+$ implies that $\omega_1$ is a $\Theta$-Berkeley cardinal

Logic 2025-03-11 v2

Abstract

Following \cite{bagaria2019large}, given cardinals κ<λ\kappa<\lambda, we say κ\kappa is a club λ\lambda-Berkeley cardinal if for every transitive set NN of size <λ<\lambda such that κN\kappa\subseteq N, there is a club CκC\subseteq \kappa with the property that for every ηC\eta\in C there is an elementary embedding j:NNj: N\rightarrow N with crit(j)=η(j)=\eta. We say κ\kappa is ν\nu-club λ\lambda-Berkeley if CκC\subseteq \kappa as above is a ν\nu-club. We say κ\kappa is λ\lambda-Berkeley if CC is unbounded in κ\kappa. We show that under AD+^+, (1) every regular Suslin cardinal is ω\omega-club Θ\Theta-Berkeley (see \rthm{main theorem}), (2) ω1\omega_1 is club Θ\Theta-Berkeley (see \rthm{main theorem lr} and \rthm{main theorem}), and (3) the δ~2n1{\tilde\delta}^1_{2n}'s are Θ\Theta-Berkeley -- in particular, ω2\omega_2 is Θ\Theta-Berkeley (see \rrem{omega2}). Along the way, we represent regular Suslin cardinals in direct limits as cutpoint cardinals (see \rthm{char extenders}). This topic has been studied in \cite{MPSC} and \cite{jackson2022suslin}, albeit from a different point of view. We also show that, assuming V=L(R)+ADV=L(\mathbb{R})+{\mathrm{AD}}, ω1\omega_1 is not Θ+\Theta^+-Berkeley, so the result stated in the title is optimal (see \rthm{lr optimal} and \rthm{thetareg optimal}).

Cite

@article{arxiv.2402.01329,
  title  = {AD$^+$ implies that $\omega_1$ is a $\Theta$-Berkeley cardinal},
  author = {Douglas Blue and Grigor Sargsyan},
  journal= {arXiv preprint arXiv:2402.01329},
  year   = {2025}
}
R2 v1 2026-06-28T14:35:44.070Z