Indestructibility and the level-by-level agreement between strong compactness and supercompactness

Indestructibility of some compactness principles over models of PFA

We show that $\mathsf{PFA}$ (Proper Forcing Axiom) implies that adding any number of Cohen subsets of $ω$ will not add an $ω_2$-Aronszajn tree or a weak $ω_1$-Kurepa tree, and moreover no $σ$-centered forcing can add a weak $ω_1$-Kurepa tree (a tree of height and size $ω_1$ with at least $ω_2$ cofinal branches). This partially answers an open problem whether ccc forcings can add $ω_2$-Aronszajn or $ω_1$-Kurepa trees. We actually prove more: We show that a consequence of $\mathsf{PFA}$, namely the guessing model principle, $\mathsf{GMP}$, which is equivalent to the ineffable slender tree proper…

Determinacy from strong compactness of $ω_1$

In the absence of the Axiom of Choice, the "small" cardinal $ω_1$ can exhibit properties more usually associated with large cardinals, such as strong compactness and supercompactness. For a local version of strong compactness, we say that $ω_1$ is $X$-strongly compact (where $X$ is any set) if there is a fine, countably complete measure on $\mathcal{P}_{ω_1}(X)$. Working in $\mathsf{ZF} + \mathsf{DC}$, we prove that the $\mathcal{P}(ω_1)$-strong compactness and $\mathcal{P}(\mathbb{R})$-strong compactness of $ω_1$ are equiconsistent with $\mathsf{AD}$ and $\mathsf{AD}_\mathbb{R} + \mathsf{DC}$…

Compactness and Comparison

Assuming an abstract comparison principle called the Ultrapower Axiom, which is motivated by the comparison process of inner model theory and generalizes the statement that the Mitchell order is linear on normal ultrafilters, we characterize strongly compact cardinals in terms of supercompactness: a strongly compact cardinal is either supercompact or a limit of supercompact cardinals. Assuming the Ultrapower Axiom and the GCH, we also prove a local result that roughly states that every countably complete ultrafilter factors as a finite iteration of supercompact ultrafilters.

Large cardinals with few measures

We show, assuming the consistency of one measurable cardinal, that it is consistent for there to be exactly kappa+ many normal measures on the least measurable cardinal kappa. This answers a question of Stewart Baldwin. The methods generalize to higher cardinals, showing that the number of lambda strong compactness or lambda supercompactness measures on P_kappa(lambda) can be exactly lambda+, if lambda>kappa is a regular cardinal. We conclude with a list of open questions. Our proofs use a critical observation due to James Cummings.

Inner models with large cardinal features usually obtained by forcing

We construct a variety of inner models exhibiting features usually obtained by forcing over universes with large cardinals. For example, if there is a supercompact cardinal, then there is an inner model with a Laver indestructible supercompact cardinal. If there is a supercompact cardinal, then there is an inner model with a supercompact cardinal κfor which 2^κ=κ^+, another for which 2^κ=κ^++ and another in which the least strongly compact cardinal is supercompact. If there is a strongly compact cardinal, then there is an inner model with a strongly compact cardinal, for which the measurable c…

The Ultrapower Axiom

The inner model problem for supercompact cardinals, one of the central open problems in modern set theory, asks whether there is a canonical model of set theory with a supercompact cardinal. The problem is closely related to the more precise question of the equiconsistency of strongly compact cardinals and supercompact cardinals. This dissertation approaches these two problems abstractly by introducing a principle called the Ultrapower Axiom which is expected to hold in all known canonical models of set theory. By investigating the consequences of the Ultrapower Axiom under the hypothesis that…

数学中小基数的紧致性：原理、后果与局限性

Compactness for small cardinals in mathematics: principles, consequences, and limitations

本文讨论小正则基数（如ω_n、ℵ_{ω+1}等）的紧致性原理，分为逻辑原理（树性质）和数学原理（图、群、拓扑空间的紧致性），重点研究这些原理在力迫扩张中的不可破坏性，并观察传统问题（如Suslin假设、Whitehead猜想）与ω_2处最强紧致性形式的独立性。

奇异后继的多段强树性质

Strong Tree Properties Along Many Segments of Successors of Singulars

该研究从大基数出发，通过力迫构造证明了ITP可在奇异基数的可数初始段后继处同时成立，并推广得到奇异基数多共尾度长段后继处的强树性质的一致性。

不可达基数 $κ$ 在 $κ^{++}$ 处具有紧致性的广义基数不变量

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

本文证明在超紧基数与弱紧基数一致的前提下，存在不可达基数 $κ$ 使得广义塔数与超滤数满足特定不等式关系，并计算了多个基数不变量的值，同时推广到传统不变量并得到不相交平稳序列性质。

奇异基数后继处的强树性质与超树性质

The Strong and Super Tree Property at Successors of Singular Cardinals

该研究聚焦奇异基数后继的强树性质与ITP（超树性质），构造通用力迫类，推广Neeman的结果，证明多种基数组合下两类性质同时成立的一致性，推进了同时在多个相继基数上获得两类树性质的问题研究。