Cosmology with the Redshift-Space Galaxy Bispectrum Monopole at One-Loop Order

TL;DR

This paper models the redshift-space galaxy bispectrum monopole at one-loop order, incorporating complex effects to improve cosmological parameter constraints, especially on bias parameters and non-Gaussianity, validated with simulations.

Contribution

It provides a comprehensive one-loop perturbation theory model for the galaxy bispectrum monopole, including all relevant effects for data comparison, and assesses its impact on cosmological constraints.

Findings

One-loop corrections extend the bispectrum modeling range.

Including one-loop greatly tightens bias parameter constraints.

Potential improvements in non-Gaussianity and $\sigma_8$ constraints are modest.

Abstract

We study the cosmological information content of the redshift-space galaxy bispectrum monopole at one-loop order in perturbation theory. We incorporate all effects necessary for comparison to data: fourth-order galaxy bias, infrared resummation (accounting for the non-linear evolution of baryon acoustic oscillations), ultraviolet counterterms, non-linear redshift-space distortions, stochastic contributions, projection, and binning effects. The model is implemented using FFTLog, and validated with the PT Challenge suite of $N$-body simulations, whose large volume allows for high-precision tests. Focusing on the mass fluctuation amplitude, $\sigma_8$, and galaxy bias parameters, we find that including one-loop corrections allow us to significantly extend the range of scales over which the bispectrum can be modeled, and greatly tightens constraints on bias parameters. However, this does not lead to noticeable improvements in the $\sigma_8$ errorbar due to the necessary marginalization over a large number of nuisance parameters with conservative priors. Analyzing a BOSS-volume likelihood, we find that the addition of the one-loop bispectrum may lead to improvements on primordial non-Gaussianity constraints by $\lesssim 30\%$ and on $\sigma_8$ by $\approx 10\%$, though we caution that this requires pushing the analysis to short scales where the galaxy bias parameters may not be correctly recovered; this may lead to biases in the recovered parameter values. We conclude that restrictive priors from simulations or higher-order statistics such as the bispectrum multipoles will be needed in order to realize the full information content of the galaxy bispectrum.