Precision analysis of the redshift-space galaxy bispectrum

We study the information content of the angle-averaged 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 perturbation theory challenge simulations, whose cumulative volume of <math display="inline"><mrow><mn>566</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>h</mi></mrow><mrow><mo>-</mo><mn>3</mn></mrow></msup><mtext> </mtext><msup><mrow><mi>Gpc</mi></mrow><mrow><mn>3</mn></mrow></msup></mrow></math> 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 <math display="inline"><mrow><msub><mrow><mi>k</mi></mrow><mrow><mi>max</mi></mrow></msub><mo>=</mo><mn>0.08</mn><mtext> </mtext><mtext> </mtext><mi>h</mi><mtext> </mtext><msup><mrow><mi>Mpc</mi></mrow><mrow><mo>-</mo><mn>1</mn></mrow></msup></mrow></math> (at <math display="inline"><mi>z</mi><mo>=</mo><mn>0.61</mn></math>). 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 <math display="inline"><mo>∼</mo><mn>3</mn><mi>σ</mi></math> level. Finally, we adjust the covariance and scale cuts to match the volume of the BOSS survey, and estimate that within the minimal <math display="inline"><mi mathvariant="normal">Λ</mi><mi>CDM</mi></math> model the bispectrum data can tighten the constraint on the mass fluctuation amplitude <math display="inline"><msub><mi>σ</mi><mn>8</mn></msub></math> by roughly 10%.