Bispectrum Modelling in Large Scale Structure - A Three Shape Model

TL;DR

This paper compares theoretical models of the matter bispectrum in large-scale structure to simulations, introducing a three-shape model that accurately fits data across scales and redshifts, and extends to primordial non-Gaussianity.

Contribution

It introduces a simple three-shape model for the matter bispectrum that improves fitting accuracy and can be extended to non-Gaussian initial conditions.

Findings

Effective field theory extends further into non-linear regime.

Two-loop perturbation theory improves accuracy range.

The three-shape model fits simulations well across scales and redshifts.

Abstract

We study the matter bispectrum of large structure by comparing theoretical models (perturbation theories and halo models) to numerical simulations using shape and amplitude correlators. We show that among the perturbation theories at one loop the effective field theory of large scale structure extends the furthest into the non-linear regime. We analyse the one and two-loop bispectra in the renormalised perturbation theory and we show that there is a significant extension in the range where results are accurate when going to two loops. In the case of the halo model, we show that there are deficiencies in the modelling of the two-halo term at redshifts z>0 that worsen in the past. Based on this observation and on the shapes identified in the halo model, we build a simple `three-shape model' that provides a good fit to N-body simulations on all scales, at both low and high redshifts. We show that this model can be easily extended to local and equilateral primordial non-Gaussianity using the same shapes.