[Paper Review] Cosmology from large-scale structure: Constraining $Λ$CDM with BOSS

Tilman Tröster, Ariel G. Sánchez+10 more|MPG.PuRe (Max Planck Society)|Sep 24, 2019

Galaxies: Formation, Evolution, Phenomena33 references46 citations

TL;DR

The paper reanalyzes BOSS DR12 anisotropic galaxy clustering with full-shape information to constrain flat ΛCDM, tests consistency with Planck, and combines with KV450 weak lensing to improve constraints and assess cross-probe tension.

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.

Motivation & Objective

• Motivate precision cosmology from low-redshift large-scale structure (LSS) measurements.
• Extract full-shape information from anisotropic galaxy clustering to constrain ΛCDM without external data.
• Assess agreement between BOSS low-redshift results and Planck CMB constraints.
• Demonstrate improvement from combining BOSS with weak lensing data (KV450).

Proposed method

• Use full anisotropic correlation function wedges from BOSS DR12 in two redshift bins (0.2≤z<0.5 and 0.5≤z<0.75).
• Model non-linear matter evolution with gRPT and a bias/RSD framework with free parameters per bin.
• Include Alcock-Paczynski rescaling to account for geometry, and fit fσ8, q⊥, q∥, and related parameters.
• Perform parameter inference with CosmoMC and CosmoSIS using uninformative priors (except Ωb h^2).
• Validate the model on simulations (Minerva, MD-Patchy mocks) and test scale cuts to ensure robustness.

Experimental results

Research questions

• RQ1 What flat ΛCDM parameter constraints can be obtained from BOSS DR12 full-shape clustering alone?
• RQ2 Do BOSS DR12 full-shape results agree with Planck CMB constraints within ΛCDM?
• RQ3 How does including weak lensing (KV450) with BOSS DR12 clustering improve parameter constraints and affect tension with Planck?
• RQ4 What is the level of tension or concordance between low-redshift probes (BOSS+KV450) and Planck in ΛCDM?

Key findings

• Ωm = 0.317^{+0.015}_{-0.019}.
• σ8 = 0.710 ± 0.049.
• h = 0.704 ± 0.024.
• BOSS+KV450 yields σ8 = 0.702 ± 0.029 and S8 = 0.728 ± 0.026.
• Odds favoring a single cosmology for low- and high-redshift probes: 7 ± 2 (Bayes factor).
• Suspiciousness log S = 0.13 ± 0.11, implying a tension of 0.76 ± 0.05 σ between low-redshift probes and Planck.
• Joint BOSS+KV450 constraints on S8 are consistent with, but 3.4σ lower than, Planck for Planck comparison.
• Low-redshift σ8 and KV450 reach tensions with Planck at ~2.1σ (suspiciousness) when combined with CMB data.