Full-shape cosmology analysis of the SDSS-III BOSS galaxy power spectrum using an emulator-based halo model: A 5% determination of σ8

We present the results obtained from the full-shape cosmology analysis of the redshift-space power spectra for four galaxy samples of the SDSS-III BOSS DR12 galaxy catalog over 0.2 <z <0.75 . For the theoretical template, we use an emulator that was built from an ensemble set of N -body simulations, which enables fast and accurate computation of the redshift-space power spectrum of "halos." Combining with the halo occupation distribution to model the galaxy-halo connection, we can compute the redshift-space power spectrum of BOSS-like galaxies in less than a CPU second, for an input model under flat Λ CDM cosmology. In our cosmology inference, we use the monopole, quadrupole, and hexadecapole moments of the redshift-space power spectrum and include seven nuisance parameters, with broad priors, to model uncertainties in the galaxy-halo connection for each galaxy sample, but do not use any information on the abundance of galaxies. We demonstrate a validation of our analysis pipeline using the mock catalogs of BOSS-like galaxies, generated using different recipes of the galaxy-halo connection and including the assembly bias effect. Assuming weak priors on cosmological parameters, except for the BBN prior on Ω_bh² and the CMB prior on n_s, we show that our model well reproduces the BOSS power spectra. Including the power-spectrum information up to k_max=0.25 h Mpc^-1, we find Ω_m=0.30 1_-0.011^+0.012, H₀=68.2 ±1.4 km s^-1 Mpc^-1, and σ₈=0.78 6_-0.037^+0.036 for the mode and 68% credible interval, after marginalization over galaxy-halo connection parameters. We find little improvement in the cosmological parameters beyond a maximum wavelength k_max≃0.2 h Mpc^-1 due to the shot noise domination and marginalization of the galaxy-halo connection parameters. Our results are consistent with the Planck CMB results within 1 σ statistical uncertainties.