Matter Power Spectra in Modified Gravity: A Comparative Study of Approximations and $N$-Body Simulations

TL;DR

This study compares various numerical and analytical methods for predicting matter power spectra in modified gravity theories, demonstrating their robustness and providing new code implementations for future cosmological surveys.

Contribution

It offers a comprehensive comparison of power spectrum predictions across multiple codes and models, and introduces new code implementations for K-mouflage and Cubic Galileon theories.

Findings

2% agreement in spectra predictions for z≤1 and k≤1 h/Mpc across models and codes

Modeling approaches are sufficiently robust for upcoming survey analyses with scale cuts

Public release of new code implementations for modified gravity theories

Abstract

Testing gravity and the concordance model of cosmology, $\Lambda$CDM, at large scales is a key goal of this decade's largest galaxy surveys. Here we present a comparative study of dark matter power spectrum predictions from different numerical codes in the context of three popular theories of gravity that induce scale-independent modifications to the linear growth of structure: nDGP, Cubic Galileon and K-mouflage. In particular, we compare the predictions from full $N$-body simulations, two $N$-body codes with approximate time integration schemes, a parametrised modified $N$-body implementation and the analytic halo model reaction approach. We find the modification to the $\Lambda$CDM spectrum is in $2\%$ agreement for $z\leq1$ and $k\leq 1~h/{\rm Mpc}$ over all gravitational models and codes, in accordance with many previous studies, indicating these modelling approaches are robust enough to be used in forthcoming survey analyses under appropriate scale cuts. We further make public the new code implementations presented, specifically the halo model reaction K-mouflage implementation and the relativistic Cubic Galileon implementation.