Orateur
Description
Small-scale galaxy clustering contains cosmological information that is complementary to standard BAO measurements and potentially highly constraining for tests of structure growth and fundamental physics. Realizing this potential, however, requires a robust treatment of the uncertain connection between galaxies and dark-matter halos. In this talk, I will present two recent studies that quantify both the opportunity and the challenge.
First, using LRG-like mock catalogs from the AbacusSummit suite spanning 81 cosmologies, we assess how strongly small-scale two-point clustering constrains cosmology under different assumptions about the galaxy–halo connection. We find a wide gap between an optimistic case in which halo occupation parameters are known and a conservative case in which they are broadly marginalized over. This result shows that small-scale clustering alone can be strongly limited by galaxy-halo degeneracies, and that informative physical or empirical priors are essential for extracting its full cosmological power.
Second, I will present forecasts for a compressed, line-of-sight-dependent three-point correlation function measured on scales below 80 Mpc. Using Roman-like ELG and DESI-like LRG mocks, we find that adding this statistic to two-point clustering substantially improves constraints on sigma_8 after marginalizing over halo occupation uncertainty. The gain is distributed across many triangle configurations and is significantly larger when line-of-sight information is retained than when only the three-point monopole is used.
Together, these results motivate higher-order, anisotropic small-scale clustering as a promising route toward more robust cosmological inference from forthcoming Roman, DESI, and related galaxy surveys.