Cosmological gravity on all scales III: non-linear matter power spectrum in phenomenological modified gravity

TL;DR

This paper validates and extends a method to accurately predict the non-linear matter power spectrum in modified gravity models, enabling precise, model-independent tests with upcoming cosmological data.

Contribution

The authors extend the ReACT approach with a new fitting function for the concentration-mass relation, achieving 1% accuracy up to k=2 h/Mpc in modified gravity scenarios.

Findings

ReACT approach validated against modified gravity simulations.

Extended with a fitting function for concentration-mass relation.

Achieves 1% accuracy in matter power spectrum predictions.

Abstract

Model-independent tests of gravity with cosmology are important when testing extensions to the standard cosmological model. To maximise the impact of these tests one requires predictions for the matter power spectrum on non-linear scales. In this work we validate the \texttt{ReACT} approach to the non-linear matter power spectrum against a suite of phenomenological modified gravity N-body simulations with a time-varying gravitational constant, covering a wider range of parameter space than previously examined. This vanilla application of \texttt{ReACT} has limited range and precision due to the different concentration-mass relation $c(M)$ that occurs when gravity is modified. We extend this approach with a fitting function for a modified concentration-mass relation, allowing for accurate (1$\%$) computation of the matter power spectrum up $k=2\,h\,{\rm Mpc}^{-1}$ across a substantial range of parameter space. This fitting function allows precision model-independent tests of modified gravity to be carried out using the data from upcoming large scale structure surveys.