# Observational status of the Galileon model general solution from cosmological data and gravitational waves

## TL;DR

This paper investigates the general solutions of the Galileon gravity model using cosmological data and gravitational wave observations, revealing significant tensions and limitations in fitting all datasets simultaneously.

## Contribution

It is the first comprehensive analysis of the full Galileon model's solutions against diverse cosmological and gravitational wave data, extending beyond previous subset constraints.

## Key findings

- Full Galileon model fits CMB spectra well
- Cubic Galileon model does not fit CMB data adequately
- GW170817 constraints rule out the full Galileon model scenarios

## Abstract

The Galileon model is a tensor-scalar theory of gravity which explains the late acceleration of the Universe expansion with no instabilities and recovers General Relativity in the strong field limit. Most constraints obtained so far on Galileon model parameters from cosmological data were derived for the limited subset of tracker solutions and reported tensions between the model and data. This paper presents the first exploration of the general solution of the Galileon model, which is confronted against recent cosmological data for both background observables and linear perturbations, using Monte-Carlo Markov chains. As representative scenarios of the Galileon models, we study the full Galileon model with disformal coupling to matter and the uncoupled cubic Galileon model. We find that the general solution of the full Galileon model provides a good fit to CMB spectra, while the cubic Galileon model does not. When extending the comparison to BAO and SNIa data, even the general solution of the full Galileon model fails at providing a good fit to all datasets simultaneously. Tensions remain if the models are extended with an additional free parameter, such as the sum of active neutrino masses or the normalization of the CMB lensing spectrum. Finally, the multi-messenger observation of GW170817 is also discussed in the framework of the scenarios considered. The time delay between the gravitational signal and its electromagnetic counterpart was computed \textit{a posteriori} in every scenario of the full Galileon model cosmological fit chains and found to be ruled out by this observation.