The one-loop matter bispectrum as a probe of gravity and dark energy

TL;DR

This paper develops a numerical framework to calculate the one-loop matter bispectrum in cosmology, enabling improved probing of gravity and dark energy effects through large-scale structure analysis.

Contribution

It introduces a flexible, perturbation theory-based method for computing the one-loop bispectrum, applicable to various modified gravity and dark energy models.

Findings

One-loop bispectrum provides more information than leading-order calculations.

The method's accuracy is comparable to non-linear fitting formulas up to certain scales.

The framework successfully tests models like DGP, $f(R)$, and dark scattering against simulations.

Abstract

Gravity-induced non-Gaussianity in the large-scale structure of the Universe, characterised by higher-order statistics such as the bispectrum (three-point cumulant), is expected to contain rich cosmological information. A measurement of the bispectrum will not only improve the cosmological constraints, but also give us the possibility to probe gravity on cosmological scales. In this paper, we present a framework to numerically calculate the one-loop matter bispectrum based on standard perturbation theory (SPT). This approach allows general modifications to the standard $\Lambda$CDM model to be easily implemented. We demonstrate the performance of the bispectrum calculation in three representative cases, namely the Vainshtein-screened Dvali-Gabadadze-Porrati (DGP) model, the chameleon-screened Hu-Sawicki $f(R)$ model and the phenomenological dark scattering (DS) momentum-exchange model. The predicted bispectra are then compared with measured results from a set of cosmological $N$-body simulations, and the impact of possible systematics arising from simplified or approximate treatments in the perturbative calculation is studied in detail. We find that the one-loop bispectrum calculation offers significantly more information on general screening and momentum exchange effects than the leading-order bispectrum calculation. Further, the accuracy of the one-loop prediction is shown to be comparable to non-linear fitting formulas over a wide range of wavenumbers ($k\lesssim0.3\,h$$\mbox{Mpc}^{-1}$) even at lower redshifts, $z\lesssim 1$.