The Halo Bispectrum in N-body Simulations with non-Gaussian Initial Conditions

TL;DR

This paper measures the halo bispectrum in N-body simulations with non-Gaussian initial conditions, showing its larger sensitivity compared to the power spectrum and assessing future constraints on primordial non-Gaussianity.

Contribution

First measurement of halo bispectrum with non-Gaussian initial conditions and comparison with perturbative predictions, highlighting the impact on squeezed configurations.

Findings

Primordial non-Gaussianity significantly affects the halo bispectrum, especially in squeezed configurations.

Good agreement between measurements and perturbative predictions at large scales.

Future galaxy surveys could constrain f_NL to a few with combined power spectrum and bispectrum analysis.

Abstract

We present measurements of the bispectrum of dark matter halos in numerical simulations with non-Gaussian initial conditions of the local type. We show, in the first place, that the overall effect of primordial non-Gaussianity on the halo bispectrum is larger than on the halo power spectrum when all measurable configurations are taken into account. We then compare our measurements with a tree-level perturbative prediction finding good agreement at large scale when the constant Gaussian bias parameter, both linear and quadratic, and their constant non-Gaussian corrections are fitted for. The best-fit values of the Gaussian bias factors and their non-Gaussian, scale-independent corrections are in qualitative agreement with the peak-background split expectations. In particular, we show that the effect of non-Gaussian initial conditions on squeezed configurations is fairly large (up to 30% for f_NL=100 at redshift z=0.5) and results from contributions of similar amplitude induced by the initial matter bispectrum, scale-dependent bias corrections as well as from nonlinear matter bispectrum corrections. We show, in addition, that effects at second order in f_NL are irrelevant for the range of values allowed by CMB and galaxy power spectrum measurements, at least on the scales probed by our simulations. Finally, we present a Fisher matrix analysis to assess the possibility of constraining primordial non-Gaussianity with future measurements of the galaxy bispectrum. We find that a survey with a volume of about 10 cubic Gpc at mean redshift z ~ 1 could provide an error on f_NL of the order of a few. This shows the relevance of a joint analysis of galaxy power spectrum and bispectrum in future redshift surveys.