Galaxies Far, Far Away: Modeling challenges for precision weak lensing and combined-probe cosmology

Galaxy surveys, which observe the positions and shapes of galaxies across large areas of the sky, can map a significant fraction of our cosmic volume. With the recent or imminent start of several next-generation projects — including LSST, Euclid, DESI, and Roman — our ability to probe the Universe is about to substantially increase. While tremendously exciting, this new era of precision presents substantial modeling challenges. I will describe how we use these observations to constrain the cosmological model and how our understanding is limited by our ability to describe the relationship between galaxies and the underlying structure. Focusing on two key astrophysical effects, galaxy intrinsic alignments and biasing, I will discuss how improved modeling has allowed us to robustly extract more information from weak lensing and combined-probe analyses in the Dark Energy Survey. I will describe both an analytic approach based on nonlinear perturbation theory and new work to develop fast, simulated-based models.