Cosmology from large-scale structure: Constraining $Λ$CDM with BOSS

TL;DR

This paper demonstrates that full-shape analysis of BOSS DR12 anisotropic galaxy clustering can tightly constrain flat $\Lambda$CDM parameters, achieving results competitive with Planck when combined with low-redshift probes. Using a gRPT-based non-linear model, a bias framework with several parameters, and robust priors, the authors derive $\Omega_m = 0.317^{+0.015}_{-0.019}$, $\sigma_8 = 0.710 \pm 0.049$, and $h = 0.704 \pm 0.024$ from BOSS alone, and $\sigma_8 = 0.702 \pm 0.029$ with KV450, yielding $S_8 = 0.728 \pm 0.026$. Bayesian consistency tests indicate Planck and BOSS are compatible within a single cosmology, while a joint BOSS+KV450 analysis reveals a mild tension with Planck on $\sigma_8$ and $S_8$, though overall low-redshift data remain informative for cross-checking CMB inferences. The work highlights the power of combining full-shape LSS with weak lensing and motivates future 3x2pt and DESI-era analyses to further probe possible new physics at late times. Overall, full-shape LSS analyses provide a robust, independent avenue to test the standard cosmological model and to explore potential extensions with upcoming surveys.

Abstract

We reanalyse the anisotropic galaxy clustering measurement from the Baryon Oscillation Spectroscopic Survey (BOSS), demonstrating that using the full shape information provides cosmological constraints that are comparable to other low-redshift probes. We find $Ω_\mathrm{m} = 0.317^{+0.015}_{-0.019}$, $σ_8 = 0.710\pm 0.049$, and $h = 0.704\pm 0.024$ for flat $Λ$CDM cosmologies using uninformative priors on $Ω_\mathrm{c}h^2$, $100θ_\mathrm{MC}$, $\ln 10^{10} A_{s}$, and $n_{s}$, and a prior on $Ω_\mathrm{b}h^2$ that is much wider than current constraints. We quantify the agreement between the Planck 2018 constraints from the cosmic microwave background and BOSS, finding the two data sets to be consistent within a flat $Λ$CDM cosmology using the Bayes factor as well as the prior-insensitive suspiciousness statistic. Combining two low-redshift probes, we jointly analyse the clustering of BOSS galaxies with weak lensing measurements from the Kilo-Degree Survey (KV450). The combination of BOSS and KV450 improves the measurement by up to 45%, constraining $σ_8 = 0.702\pm 0.029$ and $S_8 = σ_8\sqrt{Ω_\mathrm{m}/0.3} = 0.728\pm 0.026$. Over the full 5D parameter space, the odds in favour of single cosmology describing galaxy clustering, lensing, and the cosmic microwave background are $7\pm2$. The suspiciousness statistic signals a $2.1\pm0.3σ$ tension between the combined low-redshift probes and measurements from the cosmic microwave background.

Figures (9)

• Figure 1: Cosmological parameters inferred from the Minerva mocks for different choices of the minimum separation scale used in the measurement. The true cosmology is indicated with dashed lines, while the cosmological constraints are shown in red ($s_{\rm min}=15\,h^{-1}\mathrm{Mpc}$), blue ($s_{\rm min}=20\,h^{-1}\mathrm{Mpc}$), orange ($s_{\rm min}=30\,h^{-1}\mathrm{Mpc}$), and green ($s_{\rm min}=40\,h^{-1}\mathrm{Mpc}$).
• Figure 2: Constraints on the parameters $F_\mathrm{AP}$, $D_\mathrm{V}/r_{d}$, and $f\sigma_8$ at redshifts $z=0.38$ and $z=0.61$. The results from Sanchez2017 and the BOSS DR12 consensus analysis Alam2017 are shown in orange and cyan, respectively. Restricting the parameter space to flat $\Lambda$CDM in each BOSS redshift bin yields the purple contours. The joint constraints from both redshift bins (while sampling in flat $\Lambda$CDM) are shown in red. Finally, the blue contours correspond to the Planck 2018 constraints on these parameters.
• Figure 3: Constraints on flat $\Lambda$CDM derived from BOSS DR12 correlation function wedges (red) and Planck 2018 (blue).
• Figure 4: Constraints on flat $\Lambda$CDM when combining BOSS DR12 with KV450 (green). The red and blue contours are the same as Fig. \ref{['fig:cosmology-params']} and denote the constraints from BOSS and Planck alone. The constraints from KV450 are shown with dashed lines.
• Figure 5: Cosmological parameters inferred from the Minerva mocks for low-redshift sample (orange), high-redshift sample (green), and joint analysis of both samples (blue). The true cosmology is indicated with dashed lines.