Jonsson Cardinals, Erdős Cardinals, and the Core Model

Abstract

We show that every Jonsson cardinal is Ramsey in the Steel core model, provided that this model exists and there is no model with a Woodin cardinal. This basic result is improved in two directions. First, we prove the same result for delta-Jonsson and delta-Erdos cardinals, where delta is any regular cardinal smaller than kappa. These notions correspond to Jonsson and Erdos cardinals, except that the submodel or set of indiscernibles is only required to have ordertype delta. The delta-Jonsson cardinals come up in the stationary tower forcing. Second, we weaken the assumption that the Steel core model exists by showing that if the universe is a generic extension of L[\vec E] and there is no model with at Woodin cardinal then the model L[E] can take the place of the Steel core model. It follows as a corollary that if L[\vec E] is a minimal model for a Woodin cardinal then every delta-Jonsson cardinal in L[\vec E] is delta-Erdos.