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

In this paper we introduce a new public Einstein-Boltzmann solver, MGCLASS II, built as a modification of the publicly available CLASS code, that allows to obtain cosmological observables in 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. MGCLASS II is built in such a way to be compatible with parameter estimation codes such as MontePython and 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, ACDM.

Automated summary

In this paper, a new public Einstein-Boltzmann solver, MGCLASS II, is introduced as a modification of the publicly available CLASS code. It allows for obtaining cosmological observables in Modified Gravity theories and is compatible with parameter estimation codes. The results validate the predictions of this new code and provide constraints on the parameters, which show no significant deviation from the standard cosmological model.