Cosmological constraints from the nonlinear galaxy bispectrum

We present the cosmological constraints from analyzing higher-order galaxy clustering on small nonlinear scales. We use SimBIG, a forward modeling framework for galaxy clustering analyses that employs simulation-based inference to perform highly efficient cosmological inference using normalizing flows. It leverages the predictive power of high-fidelity simulations and robustly extracts cosmological information from regimes inaccessible with current standard analyses. In this work, we apply SimBIG to a subset of the BOSS galaxy sample and analyze the redshift-space bispectrum monopole, B₀(k₁,k₂,k₃), to kₘₐₓ=0.5 h/Mpc. We achieve 1σ constraints of Ωₘ=0.293_-0.027+0.027 and σ₈=0.783_-0.038+0.040, which are more than 1.2 and 2.4× tighter than constraints from standard power spectrum analyses of the same dataset. We also derive 1.4, 1.4, 1.7× tighter constraints on Ωb, h, nₛ. This improvement comes from additional cosmological information in higher-order clustering on nonlinear scales and, for σ₈, is equivalent to the gain expected from a standard analysis on a ~4× larger galaxy sample. Even with our BOSS subsample, which only spans 10% of the full BOSS volume, we derive competitive constraints on the growth of structure: S₈=0.774_-0.053+0.056. Our constraint is consistent with results from both cosmic microwave background and weak lensing. Combined with a ωb prior from big bang nucleosynthesis, we also derive a constraint on H₀=67.6_-1.8+2.2 km s^-1 Mpc^-1 that is consistent with early Universe constraints.