[Paper Review] Cosmological implications of the full shape of anisotropic clustering measurements in BOSS and eBOSS

Agne Semenaite, Ariel G. Sánchez+11 more|arXiv (Cornell University)|Nov 4, 2021

Galaxies: Formation, Evolution, Phenomena93 references49 citations

TL;DR

This paper presents a full-shape analysis of anisotropic clustering from the BOSS and eBOSS surveys, using updated non-linear matter power spectrum and non-local bias models to constrain flat ΛCDM parameters independently of the Hubble parameter. It finds excellent agreement with Planck CMB data (0.64σ tension) and reveals a 1.7σ preference for higher physical dark energy density (ωDE) when Planck priors are imposed, suggesting potential low-redshift structure growth discrepancies.

ABSTRACT

We present the analysis of the full shape of anisotropic clustering measurement from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) quasar sample together with the combined galaxy sample from the Baryon Oscillation Spectroscopic Survey (BOSS), re-analysed using an updated recipe for the non-linear matter power spectrum and the non-local bias parameters. We obtain constraints for flat $\Lambda$CDM cosmologies, focusing on the cosmological parameters that are independent of the Hubble parameter $h$. Our recovered value for the RMS linear perturbation theory variance as measured on the scale of $12\,{ m Mpc}$ is $\sigma_{12}=0.805\pm 0.049$, while using the traditional reference scale of $8\,h^{-1}{ m Mpc}$ gives $\sigma_{8}=0.815\pm 0.044$. We quantify the agreement between our measurements and the latest CMB data from Planck using the suspiciousness metric, and find them to be consistent within $0.64 \pm 0.03\sigma$. Combining our clustering constraints with the $3 imes2$pt data sample from the Dark Energy Survey (DES) Year 1 release slightly degrades this agreement to the level of $1.54 \pm 0.08\sigma$, while still showing an overall consistency with Planck. We furthermore study the effect of imposing a Planck - like prior on the parameters that define the shape of the linear matter power spectrum, and find significantly tighter constraints on the parameters that control the evolution of density fluctuations. In particular, the combination of low-redshift data sets prefers a value of the physical dark energy density $\omega_{ m DE}=0.335 \pm 0.011$, which is 1.7$\sigma$ higher than the one preferred by Planck.

Motivation & Objective

• To improve cosmological constraints from low-redshift large-scale structure by analyzing the full shape of anisotropic clustering, avoiding summary statistics like BAO and RSD.
• To update modeling of non-linear matter power spectrum and non-local bias parameters for improved accuracy in clustering predictions.
• To test internal consistency between low-redshift clustering data and Planck CMB results in the ΛCDM framework.
• To investigate parameter degeneracies and tensions, particularly in structure growth and primordial amplitude, using joint clustering and weak lensing data.
• To explore the impact of imposing Planck priors on shape parameters (ωb, ωc, ns) on constraints of evolution parameters (e.g., ωDE).

Proposed method

• Performs full-shape fitting of clustering wedges from BOSS galaxy samples and Legendre multipoles from eBOSS DR16 QSO sample in configuration space.
• Uses updated prescriptions for the non-linear matter power spectrum and non-local bias parameters, improving modeling of non-linear structure formation.
• Directly compares theoretical clustering predictions across cosmological models to observed data, bypassing RSD and BAO summary statistics.
• Focuses on cosmological parameters independent of Hubble parameter h, such as σ12, σ8, ωm, ωDE, and As.
• Combines clustering data with 3×2pt weak lensing measurements from DES Year 1 to form joint low-redshift constraints.
• Imposes Gaussian priors on Planck-derived shape parameters (ωb, ωc, ns) to assess their impact on evolution parameter constraints.

Experimental results

Research questions

• RQ1 How do full-shape clustering analyses of BOSS and eBOSS improve constraints on ΛCDM parameters compared to summary statistics?
• RQ2 What is the level of tension between low-redshift clustering data and Planck CMB measurements when using full-shape modeling?
• RQ3 How does imposing Planck priors on shape parameters affect constraints on evolution parameters like ωDE?
• RQ4 What does the data suggest about the amplitude of primordial fluctuations (As) and structure growth compared to Planck?
• RQ5 Are there systematic discrepancies in parameter combinations like Ωm–σ8 or log(1010As)–σ12 that point to inconsistencies in structure formation?

Key findings

• The RMS linear perturbation variance at 12 Mpc is σ12 = 0.805 ± 0.049, and at 8 h−1 Mpc it is σ8 = 0.815 ± 0.044.
• The agreement between clustering data and Planck CMB is consistent at 0.64 ± 0.03σ using the suspiciousness metric, indicating no significant tension.
• Combining with DES Year 1 3×2pt data increases the tension to 1.54 ± 0.08σ, though still consistent with Planck.
• Imposing Planck priors on ωb, ωc, and ns leads to significantly tighter constraints on evolution parameters, particularly ωDE.
• The joint low-redshift data prefer ωDE = 0.335 ± 0.011, which is 1.7σ higher than the Planck-preferring value, indicating a potential discrepancy in dark energy density evolution.
• The data show a preference for higher primordial amplitude (As) at fixed σ12, suggesting that low-redshift probes favor more structure growth than predicted by Planck.