Constraining M ν with the bispectrum. Part II. The information content of the galaxy bispectrum monopole

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Massive neutrinos suppress the growth of structure on small scales and leave an imprint on large-scale structure that can be measured to constrain their total mass, M ν. With standard analyses of two-point clustering statistics, M ν constraints are severely limited by parameter degeneracies. Ref. [1] demonstrated that the bispectrum, the next higher-order statistic, can break these degeneracies and dramatically improve constraints on M ν and other cosmological parameters. In this paper, we present the constraining power of the redshift-space galaxy bispectrum monopole, Bg 0. We construct the Molino suite of 75,000 mock galaxy catalogs from the Quijote N-body simulations using the halo occupation distribution (HOD) model, which provides a galaxy bias framework well-suited for simulation-based approaches. Using these mocks, we present Fisher matrix forecasts for {Ωm, Ωb, h, ns , σ8, M ν} and quantify, for the first time, the information content of the Bg 0 down to nonlinear scales. For k max = 0.5 h/Mpc, Bg 0 improves constraints on Ωm, Ωb, h, ns , σ8, and M ν by 2.8, 3.1, 3.8, 4.2, 4.2, and 4.6× over the power spectrum, after marginalizing over HOD parameters. Even with priors from Planck, Bg 0 improves all of the cosmological constraints by ≳ 2×. In fact, for Pg 0+Pg 2 and Bg 0 out to k max = 0.5 h/Mpc with Planck priors, we achieve a 1σ M ν constraint of 0.048 eV, which is tighter than the current best cosmological constraint. While effects such as survey geometry and assembly bias will have an impact, these constraints are derived for (1 h-1 Gpc)3, a substantially smaller volume than upcoming surveys. Therefore, we conclude that the galaxy bispectrum will significantly improve cosmological constraints for upcoming galaxy surveys — especially for M ν.