Extending MGCAMB tests of gravity to nonlinear scales

TL;DR

This paper extends the MGCAMB framework to include nonlinear scales using the ReACT halo model, enabling more comprehensive tests of gravity with large-scale structure data and improving constraints on modified gravity parameters.

Contribution

It introduces a nonlinear extension to MGCAMB using ReACT, allowing analysis of a broader range of data without linear scale cuts, and demonstrates improved constraints on gravity parameters.

Findings

Stronger constraints on $$ and $$ with nonlinear modeling.

Enables use of more data from large-scale structure surveys.

The nonlinear extension is publicly available on GitHub.

Abstract

Modified Growth with {\tt CAMB} ({\tt MGCAMB}) is a patch for the Einstein-Boltzmann solver {\tt CAMB} for cosmological tests of gravity. Until now, {\tt MGCAMB} was limited to scales well-described by linear perturbation theory. In this work, we extend the framework with a phenomenological model that can capture nonlinear corrections in a broad range of modified gravity theories. The extension employs the publicly available halo model reaction code {\tt ReACT}, developed for modeling the nonlinear corrections to cosmological observables in extensions of the $\Lambda$CDM model. The nonlinear extension makes it possible to use a wider range of data from large scale structure surveys, without applying a linear scale cut. We demonstrate that, with the 3$\times$2pt Dark Energy Survey data, we achieve a stronger constraint on the linear phenomenological functions $\mu$ and $\Sigma$, after marginalzing over the additional nonlinear parameter $p_1$, compared to the case without the nonlinear extension and using a linear cut. The new version of {\tt MGCAMB} is now forked with {\tt CAMB} on GitHub allowing for compatibility with future upgrades.