Cosmological Constraints on sub-horizon scales modified gravity theories with MGCLASS II

TL;DR

This paper introduces MGCLASS II, a new computational tool for analyzing cosmological data within modified gravity theories, validating it against existing models and providing new constraints on alternative theories.

Contribution

The paper presents MGCLASS II, a novel Einstein-Boltzmann solver compatible with parameter estimation codes, enabling detailed analysis of modified gravity effects on cosmology.

Findings

Good agreement with existing literature for Planck parameterizations

Original constraints on the z_flex parameterization

No significant deviation from ΛCDM found

Abstract

In this paper we introduce a new public Einstein-Boltzmann solver, \texttt{MGCLASS II}, built as a modification to the publicly available \texttt{CLASS} code, that allows to obtain cosmological observables for Modified Gravity theories. It implements several commonly used parameterizations of deviations from General Relativity, computing their impact on the growth of structure as well as on the background evolution of the Universe, together with a subset of available alternative theories, still not completely ruled out by observations. \texttt{MGCLASS II} is built in such a way to be compatible with parameter estimation codes such as \texttt{MontePython} and \texttt{Cobaya}. We exploit this possibility to constrain the parameterizations used by the Planck collaboration, in order to validate the predictions of this new code, and a newly implemented parameterization (z\_flex) which has different features. For the former we find good agreement with the results existing in the literature, while we present original constraints on the parameters of the latter, finding no significant deviation from the standard cosmological model, $\Lambda$CDM.