# Large cardinals need not be large in HOD, International Workshop on Set Theory, CIRM, Luminy, September 2014

I shall speak at the 13th International Workshop on Set Theory, held at the CIRM Centre International de Rencontres Mathématiques in Luminy near Marseille, France, September 29 to October 3, 2014.

Abstract.  I shall prove that large cardinals need not generally exhibit their large cardinal nature in HOD. For example, a supercompact cardinal need not be weakly compact in HOD, and there can be a proper class of supercompact cardinals in $V$, none of them weakly compact in HOD, with no supercompact cardinals in HOD. Similar results hold for many other types of large cardinals, such as measurable and strong cardinals. There are many open questions.

This talk will include joint work with Cheng Yong and Sy-David Friedman.

# Singular cardinals and strong extenders

• A. W. Apter, J. Cummings, and J. D. Hamkins, “Singular cardinals and strong extenders,” Central European J.~Math., vol. 11, iss. 9, pp. 1628-1634, 2013.
@article {ApterCummingsHamkins2013:SingularCardinalsAndStrongExtenders,
AUTHOR = {Apter, Arthur W. and Cummings, James and Hamkins, Joel David},
TITLE = {Singular cardinals and strong extenders},
JOURNAL = {Central European J.~Math.},
FJOURNAL = {Central European Journal of Mathematics},
VOLUME = {11},
YEAR = {2013},
NUMBER = {9},
PAGES = {1628--1634},
ISSN = {1895-1074},
MRCLASS = {03E55 (03E35 03E45)},
MRNUMBER = {3071929},
MRREVIEWER = {Samuel Gomes da Silva},
DOI = {10.2478/s11533-013-0265-1},
URL = {http://jdh.hamkins.org/singular-cardinals-strong-extenders/},
eprint = {1206.3703},
archivePrefix = {arXiv},
primaryClass = {math.LO},
}

Brent Cody asked the question whether the situation can arise that one has an elementary embedding $j:V\to M$ witnessing the $\theta$-strongness of a cardinal $\kappa$, but where $\theta$ is regular in $M$ and singular in $V$.

In this article, we investigate the various circumstances in which this does and does not happen, the circumstances under which there exist a singular cardinal $\mu$ and a short $(\kappa, \mu)$-extender $E$ witnessing “$\kappa$ is $\mu$-strong”, such that $\mu$ is singular in $Ult(V, E)$.