Cosmological Parameters from the BOSS Galaxy Power Spectrum

TL;DR

This paper measures key cosmological parameters using BOSS galaxy clustering data with a comprehensive model and MCMC analysis, providing results independent of CMB data and highlighting the importance of BAO and power spectrum shape.

Contribution

It introduces a complete perturbation theory model and employs MCMC to analyze BOSS data, offering new, direct measurements of cosmological parameters.

Findings

Measured H_0 = 67.9 ± 1.1 km/s/Mpc

Determined matter density Ω_m = 0.295 ± 0.010

Estimated fluctuation amplitude σ_8 = 0.721 ± 0.043

Abstract

We present cosmological parameter measurements from the publicly available Baryon Oscillation Spectroscopic Survey (BOSS) data on anisotropic galaxy clustering in Fourier space. Compared to previous studies, our analysis has two main novel features. First, we use a complete perturbation theory model that properly takes into account the non-linear effects of dark matter clustering, short-scale physics, galaxy bias, redshift-space distortions, and large-scale bulk flows. Second, we employ a Markov-Chain Monte-Carlo technique and consistently reevaluate the full power spectrum likelihood as we scan over different cosmologies. Our baseline analysis assumes minimal $\Lambda$CDM, varies the neutrino masses within a reasonably tight range, fixes the primordial power spectrum tilt, and uses the big bang nucleosynthesis prior on the physical baryon density $\omega_b$. In this setup, we find the following late-Universe parameters: Hubble constant $H_0=(67.9\pm 1.1)$ km$\,$s$^{-1}$Mpc$^{-1}$, matter density fraction $\Omega_m=0.295\pm 0.010$, and the mass fluctuation amplitude $\sigma_8=0.721\pm 0.043$. These parameters were measured directly from the BOSS data and independently of the Planck cosmic microwave background observations. Scanning over the power spectrum tilt or relaxing the other priors do not significantly alter our main conclusions. Finally, we discuss the information content of the BOSS power spectrum and show that it is dominated by the location of the baryon acoustic oscillations and the power spectrum shape. We argue that the contribution of the Alcock-Paczynski effect is marginal in $\Lambda$CDM, but becomes important for non-minimal cosmological models.