Precision analysis of the redshift-space galaxy bispectrum

TL;DR

This paper develops a systematic tree-level perturbation theory model for the redshift-space galaxy bispectrum, demonstrating its validity and potential to improve cosmological parameter constraints using simulated data.

Contribution

It introduces a comprehensive tree-level model including galaxy bias and nonlinear effects, validated against large-volume simulations for the first time.

Findings

Model valid up to k=0.08 h/Mpc at z=0.61

Bispectrum improves cosmological constraints by 5-15%

Potential to tighten σ8 constraints by 10% with survey data

Abstract

We study the information content of the angle-averaged (monopole) redshift space galaxy bispectrum. The main novelty of our approach is the use of a systematic tree-level perturbation theory model that includes galaxy bias, IR resummation, and also accounts for nonlinear redshift space distortions, binning, and projection effects. We analyze data from the PT challenge simulations, whose cumulative volume of 566 $h^{-3}$Gpc$^3$ allows for a precise comparison to theoretical predictions. Fitting the power spectrum and bispectrum of our simulated data, and varying all necessary cosmological and nuisance parameters in a consistent Markov chain Monte Carlo analysis, we find that our tree-level bispectrum model is valid up to $k_{\max}=0.08~h{\rm Mpc}^{-1}$ (at $z=0.61$). We also find that inclusion of the bispectrum monopole improves constraints on cosmological parameters by $(5-15)\%$ relative to the power spectrum. The improvement is more significant for the quadratic bias parameters of our simulated galaxies, which we also show to deviate from biases of the host dark matter halos at the $\sim 3\sigma$ level. Finally, we adjust the covariance and scale cuts to match the volume of the BOSS survey, and estimate that within the minimal $\Lambda$CDM model the bispectrum data can tighten the constraint on the mass fluctuation amplitude $\sigma_8$ by roughly $10\%$.