Constraining cosmological scaling solutions of a Galileon field

TL;DR

This paper investigates a Galileon scalar field model with exponential potentials that can produce scaling solutions compatible with particle physics, analyzes its perturbations, and tests it against cosmological data, finding it less effective than LambdaCDM.

Contribution

It introduces a Galileon field model with exponential potentials that generates early-time scaling solutions and thoroughly analyzes its perturbations and observational constraints.

Findings

The model produces scaling solutions compatible with matter density.

Perturbation analysis includes all relevant effects on observables.

The model does not outperform LambdaCDM in fitting data or resolving tensions.

Abstract

We study a Lagrangian with a cubic Galileon term and a standard scalar-field kinetic contribution with two exponential potentials. In this model the Galileon field generates scaling solutions in which the density of the scalar field $\phi$ scales in the same manner as the matter density at early-time. These solutions are of high interest because the scalar field can then be compatible with the energy scale of particle physics and can alleviate the coincidence problem. The phenomenology of linear perturbations is thoroughly discussed, including all the relevant effects on the observables. Additionally, we use cosmic microwave background temperature-temperature and lensing power spectra by Planck 2018, the baryon acoustic oscillations measurements from the 6dF galaxy survey and SDSS and supernovae type Ia data from Pantheon in order to place constraints on the parameters of the model. We find that despite its interesting phenomenology, the model we investigate does not produce a better fit to data with respect to $\Lambda$CDM, and it does not seem to be able to ease the tension between high and low redshift data.