# On the road to percent accuracy: nonlinear reaction of the matter power spectrum to dark energy and modified gravity

## TL;DR

This paper introduces a method combining the halo model and perturbation theory to accurately predict the nonlinear matter power spectrum for dark energy and modified gravity models, achieving better than 1% accuracy across various scenarios.

## Contribution

The authors develop a parameter-free approach that accurately predicts the nonlinear matter power spectrum for diverse dark energy and modified gravity models using existing simulations.

## Key findings

- Achieves better than 1% accuracy for dark energy models up to k ≈ 1 h/Mpc.
- Predicts the nonlinear matter power spectrum for DGP and f(R) gravity within 3% accuracy.
- Including halo mass function data improves accuracy to 1%.

## Abstract

We present a general method to compute the nonlinear matter power spectrum for dark energy and modified gravity scenarios with percent-level accuracy. By adopting the halo model and nonlinear perturbation theory, we predict the reaction of a $\Lambda$CDM matter power spectrum to the physics of an extended cosmological parameter space. By comparing our predictions to $N$-body simulations we demonstrate that with no-free parameters we can recover the nonlinear matter power spectrum for a wide range of different $w_0$-$w_a$ dark energy models to better than 1% accuracy out to $k \approx 1 \, h \, {\rm Mpc}^{-1}$. We obtain a similar performance for both DGP and $f(R)$ gravity, with the nonlinear matter power spectrum predicted to better than 3% accuracy over the same range of scales. When including direct measurements of the halo mass function from the simulations, this accuracy improves to 1%. With a single suite of standard $\Lambda$CDM $N$-body simulations, our methodology provides a direct route to constrain a wide range of non-standard extensions to the concordance cosmology in the high signal-to-noise nonlinear regime.