After a morning working on terminology and notation for the color–magnitude diagram model paper with Lauren Anderson (Flatiron), I went to two seminars. The first was Jeremy Tinker (NYU) talking about the relationship between galaxy stellar mass and dark-matter halo mass as revealed by fitting of number-count and clustering data in large-scale structure simulations. He finds that only models with extremely small scatter (less—maybe far less—than 0.18 dex) are consistent with the data, and that the result is borne out by follow-ups with galaxy–galaxy lensing and other tests. This is very hard to understand within any realistic model for how galaxies form, and constitutes a new puzzle for standard cosmology plus gastrophysics.
In the afternoon there was a very wide-ranging talk by Mark Drezde (JHU) on data-science methods for social science, intervention in health issues, and language encoding. He is interested in taking topic models and either deepening them (to make better features) or else enriching their probabilistic structure. It is all very promising, though these subjects are—despite their extreme mathematical sophistication—in their infancy.