Constraining cosmological scaling solutions of a Galileon field
  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.
