New MGCAMB tests of gravity with CosmoMC and Cobaya

TL;DR

This paper introduces an updated version of MGCAMB, a tool for testing gravity in cosmology, featuring new parameterizations, model options, and integration with Python, CosmoMC, and Cobaya for enhanced flexibility and usability.

Contribution

The paper presents a new version of MGCAMB with advanced features like cubic-spline parameterization, direct $bc$, $b3$ implementation, and compatibility with CosmoMC and Cobaya, improving cosmological gravity tests.

Findings

Enhanced flexibility in reconstructing $bc$, $b3$, and $b5$ functions.

Ability to test scalar field models coupled to dark matter.

Compatibility with Python, CosmoMC, and Cobaya for streamlined analysis.

Abstract

We present a new version of MGCAMB, a patch for the Einstein-Boltzmann solver CAMB for cosmological tests of gravity. New features include a new cubic-spline parameterization allowing for a simultaneous reconstruction of $\mu$, $\Sigma$ and the dark energy density fraction $\Omega_X$ as functions of redshift, the option to work with a direct implementation of $\mu$, $\Sigma$ (instead of converting to $\mu$, $\gamma$ first), along with the option to test models with a scalar field coupled only to dark matter, and the option to include dark energy perturbations when working with $w\ne -1$ backgrounds, to restore consistency with CAMB in the GR limit. This version of MGCAMB comes with a Python wrapper to run it directly from the Python interface, an implementation in the latest version of CosmoMC, and can be used with Cobaya.