Suppression without Thawing: Constraining Structure Formation and Dark Energy with Galaxy Clustering.

We present a new perturbative full-shape analysis of BOSS galaxy clustering data, including the full combination of the galaxy power spectrum and bispectrum multipoles, baryon acoustic oscillations, and cross-correlations with the gravitational lensing of cosmic microwave background measured from Planck. Assuming the ΛCDM model, we constrain the matter density fraction Ω_{m}=0.3138±0.0086, the Hubble constant H_{0}=68.23±0.78  km s^{-1} Mpc^{-1}, and the mass fluctuation amplitude σ_{8}=0.688±0.026 (equivalent to S_{8}=0.703±0.029). Cosmic structure at low redshifts appears suppressed with respect to the Planck ΛCDM concordance model at 4.5σ. We explore the implications of this dataset for the recent DESI BAO preference for dynamical dark energy (DDE): the BOSS data combine with DESI BAO and PantheonPlus supernovae competitively compared to the CMB, yielding no preference for DDE, but the same ∼10% suppression of structure, with dark energy being consistent with a cosmological constant at 68% CL. Our results suggest that either the data contains residual systematics, or more model-building efforts may be required to restore cosmological concordance.