Jing Zhang (Bar-Ilan University)

When does compactness imply guessing?

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Large cardinal properties, or more generally compactness principles, usually give rise to certain guessing principles. For example, if kappa is measurable, then the diamond principle at kappa holds and if kappa is supercompact, then the Laver diamond principle holds. It is a long-standing open question whether weak compactness is consistent with the failure of diamond. In the 80's, Woodin showed it is consistent that diamond fails at a greatly Mahlo cardinal, based on the analysis on Radin forcing. It turns out that this method cannot yield significant improvement to Woodin's result. In particular, we show that in any Radin forcing extension with respect to a measure sequence on kappa, if kappa is weakly compact, then the diamond principle at kappa holds. Despite the negative result, there are still some positive results obtained by refining the analysis of Radin forcing, demonstrating that diamond can fail at a strongly inaccessible cardinal satisfying strong compactness properties. Joint work with Omer Ben-Neria.